Move ($create-refentry-xref-link$) to share/sgml/freebsd.dsl
and the localized sysids to <langcode>/share/sgml/catalog.

Since <langcode>/share/sgml/freebsd.dsl still include some
language-neutral parameters and procedures for printable formats,
I will work on assorting them similarly. I am sorry that
this (and probably the next) commit may break the translation
team's usual update procedure, but you can merge the language-specific
freebsd.dsl from the English version as before.

Discussed on: -doc