Drop identityEquals from builtins, compiler and tests.

compiler/testData/diagnostics/tests/thisAndSuper/superInExtensionFunctionCall.kt

@@ -1,6 +1,9 @@
 // No supertype at all
+
+fun Any.extension(<!UNUSED_PARAMETER!>arg<!>: Any?) {}
+
 class A1 {
     fun test() {
-        <!SUPER_CANT_BE_EXTENSION_RECEIVER!>super<!>.<!DEPRECATION!>identityEquals<!>(null) // Call to an extension function
+        <!SUPER_CANT_BE_EXTENSION_RECEIVER!>super<!>.extension(null) // Call to an extension function
     }
 }