move sizeof_pkt into remote_trace_find

move sizeof_pkt into remote_trace_find

The global sizeof_pkt is only used in remote_trace_find, like so:

  reply = remote_get_noisy_reply (&(rs->buf), &sizeof_pkt);

I think in this situation it is more correct to use the recorded size
of the buffer.  Otherwise it seems that some skew could result.

	* remote.c (sizeof_pkt): Remove.
	(remote_trace_find): Use rs->buf_size, not sizeof_pkt.