emulators/virtualbox-ose: Refactor DOCS
Although the documentation builds fine currently however the doc
UserManual.pdf fails to build from the docbook with pdflatex from TeX
- So decouple the documentation file from the builds as an
additional DISTFILE. As this version is no longer supported by upstream
it is highly unlikely that the build of the documentation will be fixed
by upstream. Or unless someone has enough enthusiasm to fix the build
of the documentation once TeX 2024 hits the tree.
Approved by: portmgr (blanket)
Sponsored by: Nepustil