Deprecate nfsd fault injection

This is only useful for client testing.  I haven't really maintained it,
and reference counting and locking are wrong at this point.  You can get
some of the same functionality now from nfsd/clients/.

It was a good idea but I think its time has passed.

In the unlikely event of users, hopefully the BROKEN dependency will
prompt them to speak up.  Otherwise I expect to remove it soon.

Reported-by: Alex Lyakas <alex@zadara.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>