gdb: change remote_debug to bool

gdb: change remote_debug to bool

As far as I can see, there are no more spots looking for a remote_debug
other than true/false.  If we ever want to revert to an int, we can
always change it back later, but this makes things simpler for now.

gdb/ChangeLog:

	* remote.h (remote_debug): Change to bool.
	* remote.c (remote_debug): Change to bool.
	(_initialize_remote): Adjust.

Change-Id: I21aac5b4cff9dc4f75c8efaf47c23583ecabd2a6