Remove time-date debugging scaffolding

Problem reported by Lars Ingebrigtsen in:
https://lists.gnu.org/r/emacs-devel/2019-05/msg00721.html
* lisp/calendar/time-date.el (date-to-time):
Use plain condition-case, not condition-case-unless-debug.
1 job for master in 52 minutes and 6 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
failed #1873
test-all

00:52:06

 
Name Stage Failure
failed
test-all Test
Makefile:318: recipe for target 'check-doit' failed
make[2]: *** [check-doit] Error 1
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:293: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:957: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1