MINOR: Remove unused ProcessState.compareTo and its test (#24087)

Remove the unused `ProcessState.compareTo()` method and its
corresponding unit test.

Reviewers: Chia-Ping Tsai <chia7712@gmail.com>

group-coordinator/src/main/java/org/apache/kafka/coordinator/group/streams/assignor/ProcessState.java

@@ -200,14 +200,6 @@ public class ProcessState {
         return this.load < 1.0;
     }
 
-    public int compareTo(final ProcessState other) {
-        int loadCompare = Double.compare(this.load, other.load());
-        if (loadCompare == 0) {
-            return Integer.compare(other.capacity, this.capacity);
-        }
-        return loadCompare;
-    }
-
     public boolean hasTask(final TaskId taskId) {
         return assignedTasks.contains(taskId);
     }

group-coordinator/src/test/java/org/apache/kafka/coordinator/group/streams/assignor/ProcessStateTest.java

@@ -77,17 +77,6 @@ public class ProcessStateTest {
         assertFalse(processState.hasCapacity());
     }
 
-    @Test
-    void shouldCompareBasedOnLoadAndCapacity() {
-        ProcessState processState1 = new ProcessState("process1");
-        ProcessState processState2 = new ProcessState("process2");
-        processState1.addMember("member1");
-        processState2.addMember("member2");
-        processState1.addTask("member1", new TaskId("id1", 0), true, true);
-
-        assertTrue(processState1.compareTo(processState2) > 0);
-    }
-
     @Test
     void shouldReturnTrueIfTaskIsAssigned() {
         ProcessState processState = new ProcessState("process1");