Delete kotlin.jvm.internal.KObject

It was supposed to be used in reflection but the benefits do not outweigh the
cost of KT-6951

 #KT-3223 Fixed
 #KT-6951 Fixed

compiler/testData/asJava/lightClasses/nullabilityAnnotations/TraitClassObjectField.java

@@ -8,7 +8,7 @@ public interface TraitClassObjectField {
     @org.jetbrains.annotations.Nullable
     java.lang.String x = "";
 
-    static final class Default implements kotlin.jvm.internal.KObject {
+    static final class Default {
         @org.jetbrains.annotations.Nullable
         private final java.lang.String x = "";
         private final java.lang.String y = "";