block: Remove unused definitions

The ELV_MQUEUE_XXX definitions in include/linux/elevator.h are unused
since the removal of elevator_may_queue_fn in kernel 5.0. Remove these
definitions and also remove the documentation of elevator_may_queue_fn
in Documentiation/block/biodoc.txt.
Acked-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Documentation/block/biodoc.txt

@@ -843,11 +843,6 @@ elevator_latter_req_fn		These return the request before or after the
 
 elevator_completed_req_fn	called when a request is completed.
 
-elevator_may_queue_fn		returns true if the scheduler wants to allow the
-				current context to queue a new request even if
-				it is over the queue limit. This must be used
-				very carefully!!
-
 elevator_set_req_fn
 elevator_put_req_fn		Must be used to allocate and free any elevator
 				specific storage for a request.

include/linux/elevator.h

@@ -160,15 +160,6 @@ extern struct request *elv_rb_find(struct rb_root *, sector_t);
 #define ELEVATOR_INSERT_FLUSH	5
 #define ELEVATOR_INSERT_SORT_MERGE	6
 
-/*
- * return values from elevator_may_queue_fn
- */
-enum {
-	ELV_MQUEUE_MAY,
-	ELV_MQUEUE_NO,
-	ELV_MQUEUE_MUST,
-};
-
 #define rq_end_sector(rq)	(blk_rq_pos(rq) + blk_rq_sectors(rq))
 #define rb_entry_rq(node)	rb_entry((node), struct request, rb_node)