[Enhance](func) Delete useless code of split_by_char (#64801)

### Release note

There is a function registration part for `SPLIT_BY_CHAR` in FE, but
there is no corresponding implementation in BE.

```sql
Doris> SELECT SPLIT_BY_CHAR('apple:banana:cherry', ':');
-- ERROR 1105 (HY000): errCode = 2, detailMessage = (127.0.0.1)[INTERNAL_ERROR]Could not find function split_by_char, arg String: String, String: String return Array(Nullable(String)) 
``` 

Since the functionality of this function has already been implemented by
`SPLIT_BY_STRING`, the implementation of this function is not meaningful
and can be directly deleted.

fe/fe-core/src/main/java/org/apache/doris/catalog/BuiltinScalarFunctions.java

@@ -466,7 +466,6 @@ import org.apache.doris.nereids.trees.expressions.functions.scalar.Sm4Encrypt;
 import org.apache.doris.nereids.trees.expressions.functions.scalar.SortJsonbObjectKeys;
 import org.apache.doris.nereids.trees.expressions.functions.scalar.Soundex;
 import org.apache.doris.nereids.trees.expressions.functions.scalar.Space;
-import org.apache.doris.nereids.trees.expressions.functions.scalar.SplitByChar;
 import org.apache.doris.nereids.trees.expressions.functions.scalar.SplitByRegexp;
 import org.apache.doris.nereids.trees.expressions.functions.scalar.SplitByString;
 import org.apache.doris.nereids.trees.expressions.functions.scalar.SplitPart;
@@ -1055,7 +1054,6 @@ public class BuiltinScalarFunctions implements FunctionHelper {
             scalar(SortJsonbObjectKeys.class, "sort_jsonb_object_keys"),
             scalar(Soundex.class, "soundex"),
             scalar(Space.class, "space"),
-            scalar(SplitByChar.class, "split_by_char"),
             scalar(SplitByRegexp.class, "split_by_regexp", "regexp_split_to_array"),
             scalar(SplitByString.class, "split_by_string", "split"),
             scalar(SplitPart.class, "split_part"),

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/expressions/functions/scalar/SplitByChar.java

@@ -1,76 +0,0 @@
-// Licensed to the Apache Software Foundation (ASF) under one
-// or more contributor license agreements.  See the NOTICE file
-// distributed with this work for additional information
-// regarding copyright ownership.  The ASF licenses this file
-// to you under the Apache License, Version 2.0 (the
-// "License"); you may not use this file except in compliance
-// with the License.  You may obtain a copy of the License at
-//
-//   http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing,
-// software distributed under the License is distributed on an
-// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
-// KIND, either express or implied.  See the License for the
-// specific language governing permissions and limitations
-// under the License.
-
-package org.apache.doris.nereids.trees.expressions.functions.scalar;
-
-import org.apache.doris.catalog.FunctionSignature;
-import org.apache.doris.nereids.trees.expressions.Expression;
-import org.apache.doris.nereids.trees.expressions.functions.ExplicitlyCastableSignature;
-import org.apache.doris.nereids.trees.expressions.functions.PropagateNullable;
-import org.apache.doris.nereids.trees.expressions.shape.BinaryExpression;
-import org.apache.doris.nereids.trees.expressions.visitor.ExpressionVisitor;
-import org.apache.doris.nereids.types.ArrayType;
-import org.apache.doris.nereids.types.StringType;
-import org.apache.doris.nereids.types.VarcharType;
-
-import com.google.common.base.Preconditions;
-import com.google.common.collect.ImmutableList;
-
-import java.util.List;
-
-/**
- * ScalarFunction 'split_by_char'. This class is generated by GenerateFunction.
- */
-public class SplitByChar extends ScalarFunction
-        implements BinaryExpression, ExplicitlyCastableSignature, PropagateNullable {
-
-    public static final List<FunctionSignature> SIGNATURES = ImmutableList.of(
-            FunctionSignature.ret(ArrayType.of(VarcharType.SYSTEM_DEFAULT))
-                    .args(StringType.INSTANCE, StringType.INSTANCE)
-    );
-
-    /**
-     * constructor with 2 arguments.
-     */
-    public SplitByChar(Expression arg0, Expression arg1) {
-        super("split_by_char", arg0, arg1);
-    }
-
-    /** constructor for withChildren and reuse signature */
-    private SplitByChar(ScalarFunctionParams functionParams) {
-        super(functionParams);
-    }
-
-    /**
-     * withChildren.
-     */
-    @Override
-    public SplitByChar withChildren(List<Expression> children) {
-        Preconditions.checkArgument(children.size() == 2);
-        return new SplitByChar(getFunctionParams(children));
-    }
-
-    @Override
-    public <R, C> R accept(ExpressionVisitor<R, C> visitor, C context) {
-        return visitor.visitSplitByChar(this, context);
-    }
-
-    @Override
-    public List<FunctionSignature> getSignatures() {
-        return SIGNATURES;
-    }
-}

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/expressions/visitor/ScalarFunctionVisitor.java

@@ -486,7 +486,6 @@ import org.apache.doris.nereids.trees.expressions.functions.scalar.Sm4Encrypt;
 import org.apache.doris.nereids.trees.expressions.functions.scalar.SortJsonbObjectKeys;
 import org.apache.doris.nereids.trees.expressions.functions.scalar.Soundex;
 import org.apache.doris.nereids.trees.expressions.functions.scalar.Space;
-import org.apache.doris.nereids.trees.expressions.functions.scalar.SplitByChar;
 import org.apache.doris.nereids.trees.expressions.functions.scalar.SplitByRegexp;
 import org.apache.doris.nereids.trees.expressions.functions.scalar.SplitByString;
 import org.apache.doris.nereids.trees.expressions.functions.scalar.SplitPart;
@@ -2354,10 +2353,6 @@ public interface ScalarFunctionVisitor<R, C> {
         return visitScalarFunction(space, context);
     }
 
-    default R visitSplitByChar(SplitByChar splitByChar, C context) {
-        return visitScalarFunction(splitByChar, context);
-    }
-
     default R visitSplitByRegexp(SplitByRegexp splitByRegexp, C context) {
         return visitScalarFunction(splitByRegexp, context);
     }