build: complete the rename of get_date

* gnulib: Update to latest.
* src/date.c (includes, batch_convert, main): Track rename.
* src/touch.c (includes, get_reldate): Likewise.
* doc/coreutils.texi (Top, Date input formats): Likewise.
* bootstrap.conf (gnulib_modules): Likewise.
* doc/Makefile.am (EXTRA_DIST): Likewise.
* doc/.gitignore: Likewise.
* bootstrap: Synchronize from upstream.

bootstrap.conf

@@ -89,7 +89,6 @@ gnulib_modules="
   fsync
   ftello
   fts
-  get_date
   getgroups
   gethrxtime
   getline
@@ -154,6 +153,7 @@ gnulib_modules="
   netinet_in
   nproc
   obstack
+  parse-datetime
   pathmax
   perl
   physmem