ufs: Remove dead quota code

UFS quota is non-functional at least since 2.6.12 because dq_op was set
to NULL. Since the filesystem exists mainly to allow cooperation with Solaris
and quota format isn't standard, just remove the dead code.

CC: Evgeniy Dushistov <dushistov@mail.ru>
Signed-off-by: Jan Kara <jack@suse.cz>