Move: Do not add package directive if target package is empty

#KT-6455 Fixed

idea/testData/refactoring/move/kotlin/moveTopLevelDeclarations/misc/moveClassToDefaultPackage/after/X.kt

@@ -0,0 +1,3 @@
+class X {
+
+}

idea/testData/refactoring/move/kotlin/moveTopLevelDeclarations/misc/moveClassToDefaultPackage/after/a/main.kt

@@ -0,0 +1,5 @@
+package a
+
+class Y {
+
+}

idea/testData/refactoring/move/kotlin/moveTopLevelDeclarations/misc/moveClassToDefaultPackage/before/a/main.kt

@@ -0,0 +1,9 @@
+package a
+
+class <caret>X {
+
+}
+
+class Y {
+
+}

idea/testData/refactoring/move/kotlin/moveTopLevelDeclarations/misc/moveClassToDefaultPackage/moveClassToDefaultPackage.test

@@ -0,0 +1,5 @@
+{
+  "mainFile": "a/main.kt",
+  "type": "MOVE_KOTLIN_TOP_LEVEL_DECLARATIONS",
+  "targetPackage": ""
+}