block: bio: remove BIO_MAX_SECTORS

No one need this macro, so remove it. The motivation is for supporting
multipage bvecs, in which we only know what the max count of bvecs is
supported in the bio, instead of max size or max sectors.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Tested-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

include/linux/bio.h

@@ -42,7 +42,6 @@
 
 #define BIO_MAX_PAGES		256
 #define BIO_MAX_SIZE		(BIO_MAX_PAGES << PAGE_SHIFT)
-#define BIO_MAX_SECTORS		(BIO_MAX_SIZE >> 9)
 
 #define bio_prio(bio)			(bio)->bi_ioprio
 #define bio_set_prio(bio, prio)		((bio)->bi_ioprio = prio)