Revert "dm crypt: export sysfs of kcryptd workqueue"

This reverts commit a2b8b2d975673b1a50ab0bcce5d146b9335edfad.

WQ_SYSFS breaks the ability to reload a DM table due to sysfs kobject
collision (due to active and inactive table). Given lack of
demonstrated need for exposing this workqueue via sysfs: revert
exposing it.

Reported-by: Ignat Korchagin <ignat@cloudflare.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>