Use correct thread to remove starting window

Test: Open app, reopen app
Test: go/wm-smoke

Bug: 63784898
Bug: 64954955
Fixes: 65256018
Change-Id: I58eb90796a002cc6962efd686cef73fb36040567
diff --git a/services/core/java/com/android/server/wm/AppWindowContainerController.java b/services/core/java/com/android/server/wm/AppWindowContainerController.java
index b083aee..8b95483 100644
--- a/services/core/java/com/android/server/wm/AppWindowContainerController.java
+++ b/services/core/java/com/android/server/wm/AppWindowContainerController.java
@@ -652,7 +652,7 @@
 
             // Use the same thread to remove the window as we used to add it, as otherwise we end up
             // with things in the view hierarchy being called from different threads.
-            mHandler.post(() -> {
+            mService.mAnimationHandler.post(() -> {
                 if (DEBUG_STARTING_WINDOW) Slog.v(TAG_WM, "Removing startingView=" + surface);
                 try {
                     surface.remove();