Drop identityEquals from builtins, compiler and tests.

idea/testData/findUsages/kotlin/conventions/identityEquals.0.kt

@@ -1,16 +0,0 @@
-// PSI_ELEMENT: org.jetbrains.kotlin.psi.KtNamedFunction
-// OPTIONS: usages
-// FIND_BY_REF
-
-class A(val n: Int) {
-    override fun equals(other: Any?): Boolean = other is A && other.n == n
-}
-
-fun test() {
-    A(0) == A(1)
-    A(0) != A(1)
-    A(0) equals A(1)
-    A(0) <caret>identityEquals A(1)
-    A(0) === A(1)
-    A(0) !== A(1)
-}

idea/testData/findUsages/kotlin/conventions/identityEquals.results.txt

@@ -1,3 +0,0 @@
-Function call (13: 10) A(0) identityEquals A(1)
-Function call (14: 10) A(0) === A(1)
-Function call (15: 10) A(0) !== A(1)