nfs4file: get rid of pointless include of btrfs.h

should've been killed by "vfs: pull btrfs clone API to vfs layer"...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/nfs/nfs4file.c

@@ -8,7 +8,6 @@
 #include <linux/file.h>
 #include <linux/falloc.h>
 #include <linux/nfs_fs.h>
-#include <uapi/linux/btrfs.h>	/* BTRFS_IOC_CLONE/BTRFS_IOC_CLONE_RANGE */
 #include "delegation.h"
 #include "internal.h"
 #include "iostat.h"