Drop enum class object hack

Place valueOf() and values() into the static scope of the corresponding enum
class

 #KT-5580 Fixed
 #KT-2410 Fixed

compiler/testData/diagnostics/tests/enum/classObjectInEnum.kt

@@ -0,0 +1,9 @@
+enum class E {
+    ENTRY
+
+    class object {
+        fun entry() = ENTRY
+    }
+}
+
+fun bar() = E.entry()