BB 41739: Remove "Website appearance" from about:preferences.

It is ignored because of RFP and it is confusing for users.

browser/components/preferences/main.inc.xhtml

@@ -169,7 +169,7 @@
 </hbox>
 
 <!-- Website appearance -->
-<groupbox id="webAppearanceGroup" data-category="paneGeneral" hidden="true">
+<groupbox id="webAppearanceGroup" data-category="paneGeneral" hidden="true" data-hidden-from-search="true">
   <html:h2 data-l10n-id="preferences-web-appearance-header"/>
   <html:div id="webAppearanceSettings">
     <description class="description-deemphasized" data-l10n-id="preferences-web-appearance-description"/>