Belatedly remove the vinum(4) manual page. The vinum
manager is absent in FreeBSD since 6.0-RELEASE.

Reviewed by:	joel
Contrary to what the deleted comment said, the m_move_pkthdr()
will not smash the M_EXT and data pointer, so it is safe to
pass an mbuf with external storage procuded by m_getcl() to
m_move_pkthdr().

Reviewed by:	andre
Sponsored by:	Nginx, Inc.
- Replace compat macros with function calls.
- Remove superfluous cleaning of m_len after allocating.

Sponsored by:	Nginx, Inc.
- Replace compat macros with function calls.