refactor: factor getcompat and setcompat out of debug api.

* specs/debug_spec.yaml (getcompat, setcompat): Remove.
* lib/std/debug.lua (DEPRECATIONMSG): Use getcompat and setcompat
internally, returning an empty string if necessary.
(DEPRECATED): Don't use getcompat or setcompat now that
DEPRECATIONMSG does that.
(M): Remove getcompat and setcompat.
* lib/std/functional.lua (bind): Simplify.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>