MFC r340406:

MFC r340406:

 The roff ascii.gz documentation installed to /usr/share/doc
 was removed in r318881 when roff was removed from the base
 system.

 This results in the doc.txz distribution set containing a
 single directory (./) which is empty.

 Remove the "Additional documentation" option from the menu
 selection of bsdinstall(8), as the plain-text documentation
 installed in /usr/share/doc is installed as part of the
 packageworld target.

 The doc entry has not been removed from EXTRA_DISTRIBUTIONS
 in Makefile.inc1, in case its removal triggers an issue with
 freebsd-update(8), which is currently aware of the world/doc
 component, so the empty doc.txz continues to be created as
 a precaution.

Approved by:	re (rgrimes)
Sponsored by:	The FreeBSD Foundation