drbd: remove orphan _req_may_be_done() declaration

The _req_may_be_done() has been removed by
commit 6870ca6d ("drbd: factor out master_bio completion
and drbd_request destruction paths"), so remove the orphan
declaration.
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Acked-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>
Link: https://lore.kernel.org/r/20220920015216.782190-2-cuigaosheng1@huawei.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/drbd/drbd_req.h

@@ -266,8 +266,6 @@ struct bio_and_error {
 
 extern void start_new_tl_epoch(struct drbd_connection *connection);
 extern void drbd_req_destroy(struct kref *kref);
-extern void _req_may_be_done(struct drbd_request *req,
-		struct bio_and_error *m);
 extern int __req_mod(struct drbd_request *req, enum drbd_req_event what,
 		struct bio_and_error *m);
 extern void complete_master_bio(struct drbd_device *device,