MDL-48277 css: remove invalid @-ms-keyframes rule

This is directly copied from bootstrap, but was added to a beta version
of IE10, but never the production version so is uncessary.

Refs:
http://blogs.msdn.com/b/ie/archive/2012/06/06/moving-the-stable-web-forward-in-ie10-release-preview.aspx
https://github.com/CSSLint/csslint/issues/295

theme/base/style/core.css

@@ -2126,15 +2126,6 @@ a:hover .caret {
     }
 }
 
-@-ms-keyframes progress-bar-stripes {
-    from {
-        background-position: 40px 0;
-    }
-    to {
-        background-position: 0 0;
-    }
-}
-
 @-o-keyframes progress-bar-stripes {
     from {
         background-position: 0 0;