Don't flag invite notifications as persistent

These really don't need to be persistent, as they even stick around
when NeoChat is closed. This also spams the user's notification system
usually, if they get lots of invitations at once which don't go away
automatically.

src/notificationsmanager.cpp

@@ -249,7 +249,6 @@ void NotificationsManager::postInviteNotification(NeoChatRoom *rawRoom, const QS
     notification->setText(i18n("%1 invited you to a room", sender));
     notification->setTitle(title);
     notification->setPixmap(createNotificationImage(icon, nullptr));
-    notification->setFlags(KNotification::Persistent);
     auto defaultAction = notification->addDefaultAction(i18n("Open this invitation in NeoChat"));
     connect(defaultAction, &KNotificationAction::activated, this, [notification, room]() {
         if (!room) {