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/classObjectInEnumPrivate.kt

@@ -0,0 +1,10 @@
+enum class E {
+    ENTRY
+
+    private class object
+}
+
+fun foo() = E.values()
+fun bar() = E.valueOf("ENTRY")
+fun baz() = E.ENTRY
+fun quux() = <!INVISIBLE_MEMBER!>E<!>