io_uring/eventfd: remove unused ctx->evfd_last_cq_tail member

A previous commit got rid of any use of this member, but forgot to
remove it. Kill it.

Fixes: f4bb2f6 ("io_uring/eventfd: move ctx->evfd_last_cq_tail into io_ev_fd")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: axboe

include/linux/io_uring_types.h

@@ -442,6 +442,9 @@ struct io_ring_ctx {
 	struct list_head		defer_list;
 	unsigned			nr_drained;
 
+	/* protected by ->completion_lock */
+	unsigned			nr_req_allocated;
+
 #ifdef CONFIG_NET_RX_BUSY_POLL
 	struct list_head	napi_list;	/* track busy poll napi_id */
 	spinlock_t		napi_lock;	/* napi_list lock */
@@ -454,10 +457,6 @@ struct io_ring_ctx {
 	DECLARE_HASHTABLE(napi_ht, 4);
 #endif
 
-	/* protected by ->completion_lock */
-	unsigned			evfd_last_cq_tail;
-	unsigned			nr_req_allocated;
-
 	/*
 	 * Protection for resize vs mmap races - both the mmap and resize
 	 * side will need to grab this lock, to prevent either side from