Do not update toolbar button state inside tab 'activated' event handler

According to kmag, webextension buttons have per-tab state, so setting
the button enabled or disabled on update should be enough. Updating the
icon on tab activated may be causing performance issues.

See https://bugzilla.mozilla.org/show_bug.cgi?id=1361792 for details.

Also remove tab.active check, so that non-active tabs can catch button
updates (https://bugzilla.mozilla.org/show_bug.cgi?id=1362234#c2)

addon/webextension/background/main.js

@@ -199,7 +199,7 @@ this.main = (function() {
   }
 
   browser.tabs.onUpdated.addListener(catcher.watchFunction((id, info, tab) => {
-    if (info.url && tab.active) {
+    if (info.url) {
       if (urlEnabled(info.url)) {
         enableButton(tab.id);
       } else if (hasSeenOnboarding) {
@@ -208,20 +208,6 @@ this.main = (function() {
     }
   }, true));
 
-  browser.tabs.onActivated.addListener(catcher.watchFunction(({tabId, windowId}) => {
-    catcher.watchPromise(browser.tabs.get(tabId).then((tab) => {
-      // onActivated may fire before the url is set
-      if (!tab.url) {
-        return;
-      }
-      if (urlEnabled(tab.url)) {
-        enableButton(tabId);
-      } else if (hasSeenOnboarding) {
-        disableButton(tabId);
-      }
-    }), true);
-  }, true));
-
   communication.register("sendEvent", (sender, ...args) => {
     catcher.watchPromise(sendEvent(...args));
     // We don't wait for it to complete: