[Basilisk] Issue MoonchildProductions/UXP#1628 - Remove extensions.update.background.url from preferences

application/basilisk/app/profile/basilisk.js

@@ -155,7 +155,6 @@ pref("app.update.idletime", 60);
 //
 pref("extensions.update.enabled", true);
 pref("extensions.update.url", "https://@AM_DOMAIN@/?component=aus&@AM_AUS_ARGS@");
-pref("extensions.update.background.url", "https://@AM_DOMAIN@/?component=aus&@AM_AUS_ARGS@");
 pref("extensions.update.interval", 86400);  // Check for updates to Extensions and
                                             // Themes every day
 // Non-symmetric (not shared by extensions) extension-specific [update] preferences