fixup! Bug 21952: Implement Onion-Location

Bug 42538: Move onion icons to toolkit.

browser/components/onionservices/content/onionlocation.css

 /* Copyright (c) 2020, The Tor Project, Inc. */
 
 #onion-location-button {
-  list-style-image: url(chrome://browser/skin/onion-site.svg);
+  list-style-image: url(chrome://global/skin/icons/onion-site.svg);
   -moz-context-properties: fill;
   fill: currentColor;
 }