Bug 883397 - Remove redundant about:blank check from CustomizeMode.exit. r=Gijs

Differential Revision: https://phabricator.services.mozilla.com/D60146

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

browser/components/customizableui/CustomizeMode.jsm

@@ -497,11 +497,7 @@ CustomizeMode.prototype = {
       this.document.documentElement.removeAttribute("customizing");
 
       if (this.browser.selectedTab == gTab) {
-        if (gTab.linkedBrowser.currentURI.spec == "about:blank") {
-          closeGlobalTab();
-        } else {
-          unregisterGlobalTab();
-        }
+        closeGlobalTab();
       }
 
       let customizer = document.getElementById("customization-container");