Fix background on attachment manager

res/layout/conversation_activity_attachment_editor_stub.xml

@@ -5,7 +5,6 @@
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:gravity="center_horizontal"
-             android:background="?android:windowBackground"
              android:visibility="gone">
 
     <org.thoughtcrime.securesms.components.RemovableEditableMediaView