Bug 1493844 - part1, remove unused style for pageInfo, r=paolo

browser/base/content/pageinfo/pageInfo.css

@@ -12,10 +12,6 @@
   display: none;
 }
 
-groupbox[closed="true"] > .groupbox-body {
-  visibility: collapse;
-}
-
 #thepreviewimage {
   display: block;
 /* This following entry can be removed when Bug 522850 is fixed. */