CSS: Clean up memory leak in reliableMarginRight

Fixes gh-1795
Closes gh-1893

Thanks for the report flexphperia!
(cherry picked from commit 7d15b4d1f1)

Conflicts:
	src/css/support.js

src/css/support.js

@@ -120,6 +120,8 @@ define([
 
 			reliableMarginRightVal =
 				!parseFloat( ( window.getComputedStyle( contents, null ) || {} ).marginRight );
+
+			div.removeChild( contents );
 		}
 
 		// Support: IE8