Bug 1765821 - Remove now-redundant !important from in-content common-shared.css xul|tab styling. r=amy

Differential Revision: https://phabricator.services.mozilla.com/D144312

toolkit/themes/shared/in-content/common-shared.css

@@ -310,7 +310,7 @@ xul|tabs {
 xul|tab {
   appearance: none;
   margin-top: 0;
-  padding: 2px 20px 0 !important;
+  padding: 2px 20px 0;
   min-height: 44px;
   color: inherit;
   background-color: transparent;