Reset the preferred private JID when all resources leave a room

For example if we are talking in private with nick Joe from
room #foo, and then we leave that room, we start receiving Joe’s
message from the server-wide JID

e2e tests included!!!

src/bridge/bridge.hpp

@@ -185,6 +185,11 @@ public:
    * Remove the preferred jid for the given IRC nick
    */
   void remove_preferred_from_jid(const std::string& nick);
+  /**
+   * Given a channel_name, remove all preferred from_jid that come
+   * from this chan.
+   */
+  void remove_all_preferred_from_jid_of_room(const std::string& channel_name);
   /**
    * Add a callback to the waiting list of irc callbacks.
    */