games-puzzle/lightsoff: bump to 3.28.0

games-puzzle/lightsoff: bump to 3.28.0

* Remove unnecessary vala dep - this project is still using autotools
  and shipping pregenerated C files, thus valac is not used other than
  check for presence.
* Downgrade yelp-tools dep to itstool - yelp-tools is a developer-only
  package, so at most we'd need it with eautoreconf, if even that.
* Adapt to upstream porting from intltool to newer gettext.
* Add missing libxml2:2 build dep for gresource files xml-stripblanks
  usage, for which xmllint is used by glib-compile-resources.

Package-Manager: Portage-2.3.49, Repoman-2.3.10