Revert "Generate private constructors for Enums" cause of bootstrap problem

This reverts commit 81435c9

compiler/testData/asJava/lightClasses/DeprecatedEnumEntry.java

@@ -9,5 +9,5 @@ public enum E {
     @kotlin.Deprecated(message = "b")
     Entry3;
 
-    private E() { /* compiled code */ }
+    protected E() { /* compiled code */ }
 }

compiler/testData/codegen/bytecodeListing/inlineClasses/inlineClassTypeParametersInConstructor.txt

@@ -26,7 +26,7 @@ public final enum class TestEnum {
     public final static field ANSWER: TestEnum
     private final field z: int
     static method <clinit>(): void
-    private method <init>(p0: java.lang.String, p1: int, p2: int): void
+    protected method <init>(p0: java.lang.String, p1: int, p2: int): void
     public final method getZ(): int
     public static method valueOf(p0: java.lang.String): TestEnum
     public static method values(): TestEnum[]

compiler/testData/writeFlags/function/constructors/enum.kt

@@ -1,7 +0,0 @@
-enum class Foo {
-    A, B, C
-}
-
-// TESTED_OBJECT_KIND: function
-// TESTED_OBJECTS: Foo, <init>
-// FLAGS: ACC_PRIVATE