Remove JvmDescriptorWithExtraFlags and fix syntheticness

(of fields and classes, it is already correct for methods).

compiler/testData/writeFlags/class/visibility/internal/enum.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
 enum class MyClass() {
 }
 

compiler/testData/writeFlags/class/visibility/internal/innerEnum.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
 class Foo {
   enum class MyClass() {
   }

compiler/testData/writeFlags/class/visibility/private/enum.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
 private enum class MyClass() {
 }
 

compiler/testData/writeFlags/class/visibility/private/innerEnum.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
 // NO_FLAGS because we put enum in companion object of foo. When it will be fixed - MyClass should have ACC_PRIVATE flag
 
 class Foo {

compiler/testData/writeFlags/class/visibility/public/enum.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
 public enum class MyClass() {
 }
 

compiler/testData/writeFlags/class/visibility/public/innerEnum.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
 class Foo {
   public enum class MyClass() {
   }