Remove cleanup from remote.c

Remove cleanup from remote.c

This removes the remaining cleanup from remote.c, by changing
remote_state::buf to be a gdb::char_vector, and then fixing up all the
fallout.  The resulting patch is somewhat ugly, but on the other hand,
it eliminates some possibilities for mistakes.

Regression tested using the
Fedora-x86_64-native-extended-gdbserver-m64 builder on the buildbot.

gdb/ChangeLog
2019-01-15  Tom Tromey  <tom@tromey.com>

	* remote.c (class remote_state) <buf>: Now a char_vector.
	<buf_size>: Remove.
	(remote_target::getpkt): Change type of buf.  Remove sizeof_buf
	parameter.
	(remote_target::getpkt_or_notif_sane_1)
	(remote_target::getpkt_sane)
	(remote_target::getpkt_or_notif_sane): Likewise.
	(class remote_target) <putpkt>: New overload.
	(remote_target::read_frame): Change type of "buf_p".  Remove
	sizeof_p parameter.
	(packet_ok): New overload.
	(packet_check_result): New overload.
	Update all uses.