"abstract" modifier on enum class is an error

#KT-3454 Fixed

idea/testData/checker/Abstract.kt

@@ -116,7 +116,7 @@ enum class MyEnum() {
     <error>abstract</error> fun j() {}
 }
 
-abstract enum class MyAbstractEnum() {}
+<error>abstract</error> enum class MyAbstractEnum() {}
 
 //properties
 <error>val a: Int</error>

idea/testData/checker/regression/Jet183-1.kt

@@ -1,4 +1,4 @@
-abstract enum class ProtocolState {
+enum class ProtocolState {
   WAITING {
     override fun signal() = ProtocolState.TALKING
   }

idea/testData/checker/regression/Jet183.kt

@@ -1,4 +1,4 @@
-abstract enum class ProtocolState {
+enum class ProtocolState {
   WAITING {
     override fun signal() = ProtocolState.TALKING
   }

idea/testData/quickfix/modifiers/afterAbstractModifierInEnum.kt

@@ -0,0 +1,3 @@
+// "Make 'A' not abstract" "true"
+<caret>enum class A() {
+}

idea/testData/quickfix/modifiers/beforeAbstractModifierInEnum.kt

@@ -0,0 +1,3 @@
+// "Make 'A' not abstract" "true"
+<caret>abstract enum class A() {
+}