In the footsteps of aaf069aa, remove ACLDEBUG, which was the only
other remaining undocumented symbol in pg_config_manual.h.  The fact
that nobody had bothered to document it in seventeen years is a good
clue to its usefulness.  In practice, none of the tracing logic it
enabled would be of any value without additional effort.

Discussion: https://postgr.es/m/6631.1587565046@sss.pgh.pa.us