[ActivityPub] Properly handle Actor URIs by using events correctly

This should fix nulls on explorer lookups inputed by postman after generate_followers/getSubscribers, that I think were caused by calling common_profile_uri that, curiously, only handles local profiles

lib/util/util.php

@@ -2330,7 +2330,8 @@ function common_profile_uri($profile)
             $user = User::getKV('id', $profile->id);
             if ($user instanceof User) {
                 $uri = $user->getUri();
-            }
+            } // FIXME: might be a remote profile, by this function name, I would guess it would be fine to call this
+              // On the other hand, there's Profile->getUri
             Event::handle('EndCommonProfileURI', [$profile, &$uri]);
         }
     }