Get rid of a weird shadow background when rendering smartspace in preview

I think it has something to do ripple background, clipChildren, focusable, clickable, etc. My previous projects ran into related issues before, which is why I tried to set focusable here to false. Let me know if you have a better idea of what exactly is going on

FYI, I also did go back to my previous CL and confirmed that it's necessary.

Fixes: 152278370
Test: Factory reset the phone (with latest build and launcher built from this CL). Make sure no background is shown
Change-Id: I401ffcccd1e07a3c0beb5ed460a707d25bddf41e
diff --git a/res/layout/launcher_preview_layout.xml b/res/layout/launcher_preview_layout.xml
index 3fd02e3..4a20c70 100644
--- a/res/layout/launcher_preview_layout.xml
+++ b/res/layout/launcher_preview_layout.xml
@@ -17,7 +17,8 @@
     xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:launcher="http://schemas.android.com/apk/res-auto"
     android:layout_width="match_parent"
-    android:layout_height="match_parent">
+    android:layout_height="match_parent"
+    android:focusable="false">
 
     <com.android.launcher3.CellLayout
         android:id="@+id/workspace"