ReferenceBindingSetWrapper: use System.identityHashCode

Its just an IdentityWrapper - do not rely on ReferenceBinding
implementation.

relates to
#3452

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/lookup/ReferenceBinding.java

@@ -1210,10 +1210,6 @@ public int hashCode() {
 		: CharOperation.hashCode(this.compoundName[this.compoundName.length - 1]);
 }
 
-final int identityHashCode() {
-	return super.hashCode();
-}
-
 /**
  * Returns true if the two types have an incompatible common supertype,
  * e.g. {@code List<String>} and {@code List<Integer>}

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/lookup/ReferenceBindingSetWrapper.java

@@ -27,16 +27,15 @@ final class ReferenceBindingSetWrapper {
 
 	ReferenceBindingSetWrapper(ReferenceBinding referenceBinding) {
 		this.referenceBinding = referenceBinding;
-		this.hashCode = referenceBinding.identityHashCode();
+		this.hashCode = System.identityHashCode(referenceBinding);
 	}
 
 	@Override
 	public boolean equals(Object obj) {
 		if (obj == this) {
 			return true;
 		}
-		if (obj instanceof ReferenceBindingSetWrapper) {
-			ReferenceBindingSetWrapper other = (ReferenceBindingSetWrapper) obj;
+		if (obj instanceof ReferenceBindingSetWrapper other) {
 			return identityEqual(this.referenceBinding, other.referenceBinding);
 		}
 		return false;