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/boxWithStdlib/regressions/implicitlyCastToHashable.kt

@@ -1,11 +0,0 @@
-fun box(): String {
-    val a = true
-    val x = if (a) {
-        listOf(1)
-    }
-    else {
-        1
-    }
-    // The result of the if() above is implicitly cast to jet.Hashable, which failed before we started to map Hashable to j.l.Object
-    return "OK"
-}