Ensure non app WindowTokens are removed when closing.

Non app WindowTokens weren't propery removed when closing. This
would cause several layers to stay around in the system.

Bug: 69852584
Test: Turn phone screen off and back on again. Window is removed.
Change-Id: I51674ebdab129b462e958c3027a26ee6feeffb9f

services/core/java/com/android/server/wm/WindowToken.java

@@ -125,6 +125,11 @@ class WindowToken extends WindowContainer<WindowState> {
     }
 
     void setExiting() {
+        if (mChildren.size() == 0) {
+            super.removeImmediately();
+            return;
+        }
+
         // This token is exiting, so allow it to be removed when it no longer contains any windows.
         mPersistOnEmpty = false;