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/PrivateInClass.java

@@ -1,4 +1,4 @@
-public final class PrivateInClass implements kotlin.jvm.internal.KObject {
+public final class PrivateInClass {
     private final java.lang.String getNn() { /* compiled code */ }
 
     private final void setNn(java.lang.String value) { /* compiled code */ }