don't make locale data optional with %lang()

don't make locale data optional with %lang()

locale data is integral part of the package used to generate locale
dependant artifacts. while no %lang() might be of use in build container
it still should be possible to ie generate docs:

FAILED: doc/mpd.1 doc/mpd.conf.5
/usr/bin/sphinx-build -q -b man -d doc/man_doctrees
/home/users/builder/rpm/BUILD/mpd-0.23.5/doc doc
...
Exception occurred:
  File "/usr/share/python3.9/site-packages/babel/core.py", line 331, in
  parse
      raise UnknownLocaleError(input_id)
      babel.core.UnknownLocaleError: unknown locale 'en'