maint: silence 'time-stamp' warnings with bleeding-edge Emacs.

* contrib/tap-driver.pl:  Use "%Y" instead of "%:y" for the
'time-stamp-format' local variable.
* lib/compile: Likewise.
* lib/depcomp: Likewise.
* lib/install-sh: Likewise.
* lib/mdate-sh: Likewise.
* lib/missing: Likewise.
* lib/mkinstalldirs: Likewise.
* lib/py-compile: Likewise.
* lib/tap-driver.sh: Likewise.
* lib/test-driver: Likewise.
* lib/ylwrap: Likewise.