dirmngr: Avoid automatically checking upstream swdb.

dirmngr: Avoid automatically checking upstream swdb.

* dirmngr/dirmngr.c (housekeeping_thread): Avoid automatically
checking upstream's software database.  In Debian, software updates
should be handled by the distro mechanism, and additional upstream
checks only confuse the user.
* doc/dirmngr.texi: document that --allow-version-check does nothing.

Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
Gbp-Pq: Topic dirmngr-idling
Gbp-Pq: Name 0004-dirmngr-Avoid-automatically-checking-upstream-swdb.patch