Always listen for (re-)registration events

If we clear local storage and re-register in a foreground page, the
background page needs to re-init its websocket with the new account
credentials.

js/background.js

@@ -26,9 +26,8 @@
 
     if (textsecure.registration.isDone()) {
         init();
-    } else {
-        extension.on('registration_done', init);
     }
+    extension.on('registration_done', init);
 
     function init() {
         if (!textsecure.registration.isDone()) { return; }