Remove unused background for selection in grid_sync_item

Signed-off-by: Abdourahamane BOINAIDI <abdourahamane.boinaidi@infomaniak.com>

src/main/res/layout/grid_sync_item.xml

@@ -22,7 +22,6 @@
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:layout_gravity="center_horizontal"
-    android:background="@drawable/list_selector"
     android:gravity="center_horizontal">
 
     <com.owncloud.android.ui.SquareImageView