Fix some trivial issues reported by cppcheck

src/irc/irc_client.cpp

@@ -888,7 +888,6 @@ void IrcClient::on_unknown_message(const IrcMessage& message)
   if (message.arguments.size() < 2)
     return ;
   std::string from = message.prefix;
-  const std::string to = message.arguments[0];
   std::stringstream ss;
   for (auto it = message.arguments.begin() + 1; it != message.arguments.end(); ++it)
     {

src/xmpp/biboumi_component.cpp

@@ -579,7 +579,7 @@ void BiboumiComponent::send_ping_request(const std::string& from,
 }
 
 void BiboumiComponent::send_iq_room_list_result(const std::string& id,
-                                             const std::string to_jid,
+                                             const std::string& to_jid,
                                              const std::string& from,
                                              const std::vector<ListElement>& rooms_list)
 {

src/xmpp/biboumi_component.hpp

@@ -66,7 +66,7 @@ public:
   /**
    * Send the channels list in one big stanza
    */
-  void send_iq_room_list_result(const std::string& id, const std::string to_jid,
+  void send_iq_room_list_result(const std::string& id, const std::string& to_jid,
                                 const std::string& from,
                                 const std::vector<ListElement>& rooms_list);
   /**