Stop settings properties to null in onDestroy()

Some callbacks can come after onDestory, depending on the order in which
they were added. Setting properties to null can cause excptions in such cases.

Bug: 69812172
Change-Id: Ia812e6a074ad65591a6b5c963677a9182c45c153
diff --git a/src/com/android/launcher3/Launcher.java b/src/com/android/launcher3/Launcher.java
index 44b64d9..487c4a7 100644
--- a/src/com/android/launcher3/Launcher.java
+++ b/src/com/android/launcher3/Launcher.java
@@ -1463,7 +1463,6 @@
         } catch (NullPointerException ex) {
             Log.w(TAG, "problem while stopping AppWidgetHost during Launcher destruction", ex);
         }
-        mAppWidgetHost = null;
 
         TextKeyListener.getInstance().release();
         WallpaperColorInfo.getInstance(this).setOnThemeChangeListener(null);