Move: Remove companion object which becomes empty after the move

#KT-13903 Fixed

idea/testData/refactoring/move/kotlin/moveNestedClass/dropEmptyCompanion/after/Nested.kt

@@ -0,0 +1,3 @@
+package test
+
+class Nested{}

idea/testData/refactoring/move/kotlin/moveNestedClass/dropEmptyCompanion/after/test.kt

@@ -0,0 +1,4 @@
+package test
+
+class Test1 {
+}

idea/testData/refactoring/move/kotlin/moveNestedClass/dropEmptyCompanion/before/test.kt

@@ -0,0 +1,7 @@
+package test
+
+class Test1 {
+    companion object {
+        class <caret>Nested{}
+    }
+}

idea/testData/refactoring/move/kotlin/moveNestedClass/dropEmptyCompanion/dropEmptyCompanion.test

@@ -0,0 +1,5 @@
+{
+  "mainFile": "test.kt",
+  "type": "MOVE_KOTLIN_NESTED_CLASS",
+  "withRuntime": "true"
+}