Delete Hashable, pull up its members to Any

Extensions on nullable types remain in Library.kt

 #KT-1741 Obsolete
 #KT-2805 Obsolete
 #KT-1365 Fixed
 #KT-4517 In Progress

compiler/testData/codegen/box/package/checkCast.kt

@@ -1,5 +1,5 @@
 class C(val x: Int) {
-  fun equals(rhs: Any?): Boolean {
+  override fun equals(rhs: Any?): Boolean {
     if (rhs is C) {
       val rhsC = rhs as C
       return rhsC.x == x