security/openssh-portable: Remove groff dependency

An unconditional dependency on groff was added in ports r441907 [1] as part
of bug 213725 (groff removal from base). OpenSSH release-5.7 notes the
following:

• Use mandoc as preferred manpage formatter if it is present, followed by nroff and groff respectively.

This change removes groff as an unconditional dependency allowing mandoc
to be used, and reduces many subsequence dependencies accordingly.

It additionally explicitly sets 'mantype', which ensures that man pages
are installed in the same location (LOCALBASE/man) independently from the
generator used. Without this, a packaging (pkg-plist) error is observed
(installing man pages into LOCALBASE/doc not LOCALBASE/man), which was
presumably the genesis of the groff dependency addition in the first place.

[1] http://svnweb.freebsd.org/changeset/ports/441907

Reviewed by: bdrewery (maintainer), allanjude
Approved by: bdrewery (maintainer)
Differential Revision: D11793