btrfs: optmize listxattr

The ->list handler is really not useful at all, because we always call
btrfs_xattr_generic_list anyway.  After this is done
find_btrfs_xattr_handler becomes unused, and it becomes obvious that the
temporary name buffer allocation isn't needed but we can directly copy
into the supplied buffer.

Tested with various getfattr -d calls on varying xattr lists.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/xattr.h

@@ -47,12 +47,4 @@ ssize_t btrfs_xattr_get(struct inode *inode, int name_index, const char *name,
 int btrfs_xattr_set(struct inode *inode, int name_index, const char *name,
 			const void *value, size_t size, int flags);
 
-/*
- * the only reason this is public is for acl.c.  There may be a point where
- * acl.c doesn't need it, and if thats the case we need to remove it and make
- * it static in xattr.c
- */
-size_t btrfs_xattr_generic_list(struct inode *inode, char *list,
-				size_t list_size, const char *name,
-				size_t name_len);
 #endif /* __XATTR__ */