Bug 1441878 - Remove unused css variable theme-codemirror-gutter-background;r=ntim

This variable is no longer used anywhere and can be removed

Differential Revision: https://phabricator.services.mozilla.com/D4309

--HG--
extra : moz-landing-system : lando

browser/base/content/test/static/browser_parsable_css.js

@@ -100,9 +100,6 @@ let propNameWhitelist = [
   // Bug 1441929
   {propName: "--theme-search-overlays-semitransparent",
    isFromDevTools: true},
-  // Bug 1441878
-  {propName: "--theme-codemirror-gutter-background",
-   isFromDevTools: true},
   // These custom properties are retrieved directly from CSSOM
   // in videocontrols.xml to get pre-defined style instead of computed
   // dimensions, which is why they are not referenced by CSS.

devtools/client/themes/variables.css

@@ -102,7 +102,6 @@
   --theme-arrowpanel-dimmed-further: hsla(0,0%,80%,.45);
   --theme-arrowpanel-disabled-color: GrayText;
 
-  --theme-codemirror-gutter-background: #f4f4f4;
   --theme-messageCloseButtonFilter: invert(0);
 }
 
@@ -205,7 +204,6 @@
   --theme-arrowpanel-dimmed-further: rgba(249,249,250,.15);
   --theme-arrowpanel-disabled-color: rgba(249,249,250,.5);
 
-  --theme-codemirror-gutter-background: #262b37;
   --theme-messageCloseButtonFilter: invert(1);
 }