Bug 1720441 - Remove unthemed menubar color. r=stransky

Menubars on Linux are unthemed by default so they are transparent. Only
themed menubars should use -moz-menubarcolor.

Differential Revision: https://phabricator.services.mozilla.com/D119873

browser/themes/linux/places/organizer.css

@@ -7,6 +7,7 @@
 #placesToolbar {
   appearance: auto;
   -moz-default-appearance: menubar;
+  color: -moz-menubartext;
 }
 
 @media (-moz-menubar-drag) {

toolkit/themes/linux/global/menu.css

@@ -51,10 +51,6 @@ menucaption[disabled="true"] {
   color: GrayText;
 }
 
-menubar {
-  color: -moz-menubartext;
-}
-
 menubar > menu {
   padding: 0 4px;
 }