block/bfq: remove unused bfq_class_rt which never used

This macro is never used after introduced from commit aee69d78
("block, bfq: introduce the BFQ-v0 I/O scheduler as an extra scheduler")

Better to remove it.
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Paolo Valente <paolo.valente@linaro.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bfq-iosched.c

@@ -427,7 +427,6 @@ void bfq_schedule_dispatch(struct bfq_data *bfqd)
 }
 
 #define bfq_class_idle(bfqq)	((bfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
-#define bfq_class_rt(bfqq)	((bfqq)->ioprio_class == IOPRIO_CLASS_RT)
 
 #define bfq_sample_valid(samples)	((samples) > 80)