btrfs: prune unused includes

Remove includes if none of the interfaces and exports is used in the
given source file.

Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ordered-data.c

@@ -6,7 +6,6 @@
 #include <linux/slab.h>
 #include <linux/blkdev.h>
 #include <linux/writeback.h>
-#include <linux/pagevec.h>
 #include "ctree.h"
 #include "transaction.h"
 #include "btrfs_inode.h"