chore: improve 'control preference' designer

Adds a "Remove '<key>'" preview

Author: david-allison

AnkiDroid/src/main/res/layout/control_preference.xml

@@ -57,5 +57,6 @@
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:divider="@null"
+        tools:listitem="@layout/control_preference_list_item"
         />
 </LinearLayout>