btrfs: remove unnecessary prototype declarations at disk-io.c

We have a few static functions at disk-io.c for which we have a forward
declaration of their prototype, but it's not needed because all those
functions are defined before they are called, so remove them.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -60,15 +60,6 @@
 				 BTRFS_SUPER_FLAG_METADUMP |\
 				 BTRFS_SUPER_FLAG_METADUMP_V2)
 
-static void btrfs_destroy_ordered_extents(struct btrfs_root *root);
-static int btrfs_destroy_delayed_refs(struct btrfs_transaction *trans,
-				      struct btrfs_fs_info *fs_info);
-static void btrfs_destroy_delalloc_inodes(struct btrfs_root *root);
-static int btrfs_destroy_marked_extents(struct btrfs_fs_info *fs_info,
-					struct extent_io_tree *dirty_pages,
-					int mark);
-static int btrfs_destroy_pinned_extent(struct btrfs_fs_info *fs_info,
-				       struct extent_io_tree *pinned_extents);
 static int btrfs_cleanup_transaction(struct btrfs_fs_info *fs_info);
 static void btrfs_error_commit_super(struct btrfs_fs_info *fs_info);