Bug 1581399 - Remove useless rule in svg.css. r=longsonr

It was added in bug 256624, but -moz-binding is no longer exposed to content so
it doesn't do anything.

Differential Revision: https://phabricator.services.mozilla.com/D45954

--HG--
extra : moz-landing-system : lando

layout/svg/svg.css

@@ -36,10 +36,6 @@ symbol:-moz-use-shadow-tree-root {
   display: inline !important;
 }
 
-switch {
- -moz-binding: none !important;
-}
-
 svg:not(:root), symbol, image, marker, pattern, foreignObject {
  overflow: hidden;
 }