gdb_is_target_remote -> gdb_protocol_is_remote

gdb_is_target_remote -> gdb_protocol_is_remote

This is similar to the previous patch, but for gdb_protocol_is_remote.

gdb_is_target_remote and its MI cousin mi_is_target_remote, use "maint
print target-stack", which is unnecessary when checking whether
gdb_protocol is "remote" or "extended-remote" would do.  Checking
gdb_protocol is more efficient, and can be done before starting GDB
and running to main, unlike gdb_is_target_remote/mi_is_target_remote.

This adds a new gdb_protocol_is_remote procedure, and uses it in place
of gdb_is_target_remote/mi_is_target_remote throughout.

There are no uses of gdb_is_target_remote/mi_is_target_remote left
after this.  Those will be eliminated in a following patch.

In some spots, we no longer need to defer the check until after
starting GDB, so the patch adjusts accordingly.

Change-Id: I90267c132f942f63426f46dbca0b77dbfdf9d2ef
Approved-By: Tom Tromey <tom@tromey.com>