LU-13004 gnilnd: remove support for GNILND_BUF_VIRT_*

LU-13004 gnilnd: remove support for GNILND_BUF_VIRT_*

GNILND_BUF_VIRT_UNMAPPED and GNILND_BUF_VIRT_MAPPED are
not longer set, so remove them and any code that only
runs when they are set.
    gnd_map_nvirt  gnd_map_virtnob
can go too.

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: If394bc2cf64f903ed4cdb1e1e80a2a017accd562
Reviewed-on: https://review.whamcloud.com/37847
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>