don't change side controllers when reassigning sides.

the bug which was fixed by this code (https://gna.org/bugs/?13038)
shouldn't happen anymore becasue droiding sides now only changes the
proxy controller.

src/server/game.cpp

@@ -572,7 +572,6 @@ void game::change_controller(const size_t side_index,
 		if (started_) {
 			send_and_record_server_message(player_name + " takes control of side " + side + ".");
 		}
-		side_controllers_[side_index] = "human";
 	}
 
 	simple_wml::document response;