Treat procedural languages as owned by the bootstrap superuser, rather

Treat procedural languages as owned by the bootstrap superuser, rather
than owned by nobody.  This results in cleaner display of language ACLs,
since the backend's aclchk.c uses the same convention.  AFAICS there is
no practical difference but it's nice to avoid emitting SET SESSION
AUTHORIZATION; also this will make it easier to transition pg_dump to
some future version in which we may include an explicit ownership column
in pg_language.  Per gripe from David Begley.