intl: Stop installing ChangeLog.inst

intl: Stop installing ChangeLog.inst

After the git-version-gen migration (commit fbf4e276), the
creation of gettext-tools/intl/ChangeLog.inst in configure.ac was
removed because we lost access to $RELEASE_DATE.  Given that
intl/VERSION provides enough information, simply drop the
ChangeLog file.
Problem reported by Bruce Korb in
<https://lists.gnu.org/archive/html/bug-gettext/2014-06/msg00022.html>.
* Makefile.in (install-data): Don't install ChangeLog.inst.
(distclean): Don't remove ChangeLog.inst.
(uninstall): Don't remove ChangeLog under $(gettextsrcdir)/intl.
(dist): Don't include ChangeLog in the distribution.