dedupe: cleanups and rate estimation

Signed-off-by: Jens Axboe <axboe@fb.com>
dedupe: remove rb_lock when done

Signed-off-by: Jens Axboe <axboe@fb.com>
dedupe: print threads used up front

Signed-off-by: Jens Axboe <axboe@fb.com>