Simplify a few timestamps

Simplify a few timestamps

* lisp/calendar/time-date.el (safe-date-to-time):
* lisp/calendar/timeclock.el (timeclock-generate-report):
* lisp/epg.el (epg--start):
* lisp/gnus/gnus-demon.el (gnus-demon-nntp-close-connection):
* lisp/gnus/gnus-util.el (gnus-date-get-time):
* lisp/gnus/nnheader.el (nnheader-last-message-time):
* lisp/gnus/nnrss.el (nnrss-request-expire-articles):
* lisp/vc/ediff-util.el (ediff-command-begin-time)
(ediff-calc-command-time, ediff-profile):
Prefer an integer like 0 to a timestamp list like (0 0)
where either will do.