Prefer nil to (current-time) when either works

Prefer nil to (current-time) when either works

* doc/misc/gnus.texi (Category Syntax):
* lisp/allout-widgets.el (allout-widgets-post-command-business):
* lisp/cedet/ede/detect.el (ede-detect-qtest):
* lisp/cedet/pulse.el (pulse-momentary-highlight-overlay)
(pulse-tick):
* lisp/cedet/semantic.el (bovinate):
* lisp/cedet/semantic/analyze.el:
(semantic-analyze-current-symbol-default, semantic-adebug-analyze):
* lisp/cedet/semantic/analyze/refs.el (semantic-analyze-current-tag):
* lisp/cedet/semantic/lex.el (semantic-lex-test):
* lisp/cedet/semantic/symref/filter.el:
(semantic-symref-test-count-hits-in-tag):
* lisp/cedet/srecode/dictionary.el (srecode-adebug-dictionary):
* lisp/cedet/srecode/map.el (srecode-adebug-maps):
* lisp/desktop.el (desktop-create-buffer):
* lisp/emacs-lisp/benchmark.el (benchmark-elapse):
* lisp/emacs-lisp/elp.el (elp--make-wrapper):
* lisp/epa.el (epa--show-key):
* lisp/erc/erc.el (erc-lurker-cleanup, erc-lurker-p):
* lisp/gnus/gnus-agent.el (gnus-agent-fetch-articles)
(gnus-agent-expire-group-1, gnus-agent-store-article):
* lisp/gnus/gnus-art.el (article-lapsed-string):
* lisp/gnus/gnus-cloud.el (gnus-cloud-update-newsrc-data)
(gnus-cloud-collect-full-newsrc):
* lisp/gnus/gnus-group.el (gnus-group-timestamp-delta):
* lisp/gnus/gnus-html.el (gnus-html-cache-expired):
* lisp/gnus/gnus-score.el (gnus-score-load-file)
(gnus-decay-scores):
* lisp/gnus/nndiary.el (nndiary-expired-article-p):
* lisp/gnus/nnmail.el (nnmail-expired-article-p):
* lisp/gnus/nnmaildir.el (nnmaildir--scan):
* lisp/gnus/score-mode.el (gnus-score-edit-insert-date):
* lisp/image/gravatar.el (gravatar-cache-expired):
* lisp/net/newst-backend.el (newsticker--image-get)
(newsticker--cache-mark-expired):
* lisp/nxml/rng-maint.el (rng-time-function):
* lisp/org/org-agenda.el (org-agenda-to-appt):
* lisp/org/org-clock.el (org-clock-resolve-clock)
(org-clock-resolve, org-resolve-clocks-if-idle):
* lisp/org/org-colview.el (org-columns-edit-value, org-columns)
(org-columns-compute-all, org-agenda-columns):
* lisp/org/org-element.el (org-element--cache-interrupt-p)
(org-element--cache-sync):
* lisp/org/org-habit.el (org-habit-get-faces)
(org-habit-insert-consistency-graphs):
* lisp/org/org-indent.el (org-indent-add-properties):
* lisp/org/org-timer.el (org-timer-start)
(org-timer-pause-or-continue, org-timer-seconds)
(org-timer-show-remaining-time, org-timer-set-timer):
* lisp/org/org.el (org-babel-load-file, org-current-time)
(org-today, org-auto-repeat-maybe, org-read-date-analyze)
(org-small-year-to-year, org-goto-calendar):
* lisp/org/ox.el (org-export-insert-default-template):
* lisp/time.el (emacs-uptime):
* lisp/type-break.el (type-break-mode, type-break)
(type-break-time-warning-schedule, type-break-check):
* lisp/url/url-cache.el (url-cache-expired):
* lisp/url/url.el (url-retrieve-synchronously):
* test/lisp/char-fold-tests.el (char-fold--speed-test):
* test/manual/cedet/semantic-ia-utest.el:
(semantic-symref-test-count-hits-in-tag):
* test/manual/cedet/semantic-tests.el (semantic-idle-pnf-test)
(semantic-lex-test-full-depth):
Use nil instead of (current-time) where either will do, as nil is
a bit more efficient and should have less timing error.