LU-13004 lustre: remove support for KVEC bulk descriptors

LU-13004 lustre: remove support for KVEC bulk descriptors

KVEC descriptors are no long used nor needed.
KIOV are sufficient for all needs.

This allows us to remove
  PTLRPC_BULK_BUF_KVEC
and
  PTLRPC_BULK_BUF_KIOV
flags - the distinction no longer exists.

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: Ic3a6ec942b60a05c7ce6c5b05659700e1399d0b9
Reviewed-on: https://review.whamcloud.com/36971
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>