btrfs: remove stale define after removing ordered operations

Last user removed in commit "btrfs: disable strict file flushes for
renames and truncates" (8d875f95da).

Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/ctree.h

@@ -62,13 +62,6 @@ struct btrfs_ordered_sum;
 
 #define BTRFS_COMPAT_EXTENT_TREE_V0
 
-/*
- * files bigger than this get some pre-flushing when they are added
- * to the ordered operations list.  That way we limit the total
- * work done by the commit
- */
-#define BTRFS_ORDERED_OPERATIONS_FLUSH_LIMIT (8 * 1024 * 1024)
-
 /* holds pointers to all of the tree roots */
 #define BTRFS_ROOT_TREE_OBJECTID 1ULL