block, bfq: remove unused variable for bfq_queue

it defined in d0edc247, but there's nowhere to use it,
so remove it.
Signed-off-by: Yuwei Guan <Yuwei.Guan@zeekrlife.com>
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20221018030139.159-1-Yuwei.Guan@zeekrlife.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/bfq-iosched.h

@@ -369,12 +369,8 @@ struct bfq_queue {
 	unsigned long split_time; /* time of last split */
 
 	unsigned long first_IO_time; /* time of first I/O for this queue */
-
 	unsigned long creation_time; /* when this queue is created */
 
-	/* max service rate measured so far */
-	u32 max_service_rate;
-
 	/*
 	 * Pointer to the waker queue for this queue, i.e., to the
 	 * queue Q such that this queue happens to get new I/O right