FBSD: remove vestiges of Giant

FBSD: remove vestiges of Giant

We do not support versions of FreeBSD that used Giant to
serialize access to vnode fields, and we always use the same locking
(which really ought to be MPSAFE).  Always set the MPSAFE flags
as needed, and do not bother to call VFS_[UN]LOCK_GIANT which
will never do anything for us.

Reviewed-on: http://gerrit.openafs.org/3656
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 3c91f1d88165dca085a26b87f2c0148e84e179d2)

Change-Id: I7709c886da933023a48ae368373e31f131539d42
Reviewed-on: http://gerrit.openafs.org/3679
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>