dirmngr: Use a longer timer tick interval.

* dirmngr/dirmngr.c (TIMERTICK_INTERVAL): Always use 60 seconds like
we did for WindowsCE.

Given that the timer tick is only used for housekeeping tasks and
these are done every 10 minutes, it makes no sense to use 2 seconds.
The minor drawback is tha the housekeeping may be delayed by one
minute.

NB: For the purpose of power saving, we already make sure that the
process wakes up at the full second so that it is synchronized to the
wakeup time of other processes.

• Signed-off-by: Werner Koch <wk@gnupg.org>