io_uring: remove dead REQ_F_SEQ_PREV flag

With the conversion to io-wq, we no longer use that flag. Kill it.

Fixes: 561fb04a ("io_uring: replace workqueue usage with io-wq")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -340,7 +340,6 @@ struct io_kiocb {
 #define REQ_F_NOWAIT		1	/* must not punt to workers */
 #define REQ_F_IOPOLL_COMPLETED	2	/* polled IO has completed */
 #define REQ_F_FIXED_FILE	4	/* ctx owns file */
-#define REQ_F_SEQ_PREV		8	/* sequential with previous */
 #define REQ_F_IO_DRAIN		16	/* drain existing IO first */
 #define REQ_F_IO_DRAINED	32	/* drain done */
 #define REQ_F_LINK		64	/* linked sqes */