Drop a hack which allowed to make Unit an object

compiler/testData/builtin-classes.txt

@@ -1278,16 +1278,6 @@ public abstract class Number {
     public abstract fun toShort(): kotlin.Short
 }
 
-private open class OldUnit {
-    /*primary*/ public constructor OldUnit()
-
-    private class object <class-object-for-OldUnit> {
-        /*primary*/ private constructor <class-object-for-OldUnit>()
-        public final val VALUE: kotlin.Unit
-            public final fun <get-VALUE>(): kotlin.Unit
-    }
-}
-
 public trait Progression</*0*/ out N : kotlin.Any> : kotlin.Iterable<N> {
     public abstract val end: N
         public abstract fun <get-end>(): N
@@ -1473,16 +1463,8 @@ public open class Throwable {
     public final fun printStackTrace(): kotlin.Unit
 }
 
-public object Unit : kotlin.OldUnit {
+public object Unit {
     /*primary*/ private constructor Unit()
-    public final val VALUE: kotlin.Unit
-        public final fun <get-VALUE>(): kotlin.Unit
-    
-    public class object <class-object-for-Unit> : kotlin.Unit {
-        /*primary*/ private constructor <class-object-for-Unit>()
-        public final override /*1*/ /*fake_override*/ val VALUE: kotlin.Unit
-            public final override /*1*/ /*fake_override*/ fun <get-VALUE>(): kotlin.Unit
-    }
 }
 
 public final annotation class data : kotlin.Annotation {

core/builtins/src/kotlin/Unit.kt

@@ -16,16 +16,6 @@
 
 package kotlin
 
-// Temporary class for backward compatibility with Java code
+public object Unit {
-private open class OldUnit() {
-    class object {
-        public val VALUE: Unit = Unit
-    }
-}
-
-public object Unit : OldUnit() {
-    public val VALUE: Unit
-        get() = this
-
     override fun toString() = "kotlin.Unit"
 }