rtsp-stream: Removing unvailed transports returns false

When removing transports the assertion was that the transport passed in for removal was present in the list however that can be assumed. As an example if a transport was removed from send_tcp_message for being unable to be contacted, the main thread can try to remove the same transport again if it gets a handle_pause_request. This will not effect the transport list however will effect n_tcp_transports as it will be decrement twice and there for show the wrong value.