Prohibit inner classes in objects

Using inner classes in objects makes little sense since objects have single static instance

compiler/testData/loadJava/compiledKotlin/annotations/classes/ClassInClassObject.kt

@@ -5,7 +5,5 @@ annotation class Anno
 class Class {
     class object {
         Anno class Nested
-
-        Anno inner class Inner
     }
 }

compiler/testData/loadJava/compiledKotlin/annotations/classes/ClassInClassObject.txt

@@ -10,10 +10,6 @@ internal final class Class {
     internal class object Default {
         /*primary*/ private constructor Default()
 
-        test.Anno() internal final inner class Inner {
-            /*primary*/ public constructor Inner()
-        }
-
         test.Anno() internal final class Nested {
             /*primary*/ public constructor Nested()
         }