Generate equals/hashCode(): Enable for classes without properties

Also:
- forbid for enum classes
- use javaClass.hashCode() instead of 0 if class has no properties

 #KT-18418 Fixed

idea/testData/codeInsight/generate/equalsWithHashCode/explicitDefaultAccessors.kt

@@ -5,6 +5,4 @@ class Test {
     var name: String = ""
         get
     <caret>
-}
-
-// FORCED
+}