Bug 1195517 - Remove unused ic_menu_quit from gecko_app. r=liuche

This doesn't appear in Fennec builds and I don't know which web apps "quit"
could appear in so I didn't test this in a web app. I can confirm no issues
with a typical Fennec build, however.

--HG--
extra : commitid : LbNepxFEs3P
extra : rebase_source : 687af1c7750c4fb0f3c866dfcaae8291494e146c

mobile/android/base/resources/menu/gecko_app_menu.xml

@@ -5,7 +5,6 @@
 
 <menu xmlns:android="http://schemas.android.com/apk/res/android">
     <item android:id="@+id/quit"
-          android:icon="@drawable/ic_menu_quit"
           android:title="@string/quit"
           android:orderInCategory="10" />
 </menu>