Bug 1598516 - Remove isLocalAboutURI since all about: URIs are local. r=Gijs

With DocumentChannel, the 'URI' of the channel that we proxy for RemoteWebProgress doesn't have the resolved URI, and reports the about: version instead.

All about: URIs are local these days, so we can just check for that scheme directly, and simplify the code.

Differential Revision: https://phabricator.services.mozilla.com/D54251

browser/modules/AsyncTabSwitcher.jsm

@@ -374,9 +374,7 @@ class AsyncTabSwitcher {
       // determined by the busy state on the tab element and checking
       // if the loaded URI is local.
       let isBusy = this.requestedTab.hasAttribute("busy");
-      let isLocalAbout = this.tabbrowser.isLocalAboutURI(
-        requestedBrowser.currentURI
-      );
+      let isLocalAbout = requestedBrowser.currentURI.schemeIs("about");
       let hasSufficientlyLoaded = !isBusy && !isLocalAbout;
 
       let fl = requestedBrowser.frameLoader;