afs: Do not supply bogus poll vnodeops for FBSD

afs: Do not supply bogus poll vnodeops for FBSD

We currently provide one which just always returns 1, but the
kernel provides a vop_nopoll which conceptually is the same thing.
That one, however, provides some feature checks and fails when
consumers ask for fancy features that are not portable.

Change-Id: Iba03904aac2883e18a1abdd4f09289b6c6f907c0
Reviewed-on: http://gerrit.openafs.org/11882
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams <3chas3@gmail.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>