It is not used anymore since commit 
957780eb2788d8 ("Btrfs: introduce
ticketed enospc infrastructure"), so just remove it.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
        spin_lock_init(&space_info->lock);
        space_info->flags = flags & BTRFS_BLOCK_GROUP_TYPE_MASK;
        space_info->force_alloc = CHUNK_ALLOC_NO_FORCE;
-       init_waitqueue_head(&space_info->wait);
        INIT_LIST_HEAD(&space_info->ro_bgs);
        INIT_LIST_HEAD(&space_info->tickets);
        INIT_LIST_HEAD(&space_info->priority_tickets);
 
        struct rw_semaphore groups_sem;
        /* for block groups in our same type */
        struct list_head block_groups[BTRFS_NR_RAID_TYPES];
-       wait_queue_head_t wait;
 
        struct kobject kobj;
        struct kobject *block_group_kobjs[BTRFS_NR_RAID_TYPES];