vfs: delete vfs_readdir function declaration

vfs_readdir() was replaced by iterate_dir() in commit 5c0ba4e0762e
("[readdir] introduce iterate_dir() and dir_context").

Signed-off-by: Zhang Zhen <zhenzhang.zhang@huawei.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/fs.h

@@ -2684,7 +2684,6 @@ void inode_sub_bytes(struct inode *inode, loff_t bytes);
 loff_t inode_get_bytes(struct inode *inode);
 void inode_set_bytes(struct inode *inode, loff_t bytes);
 
-extern int vfs_readdir(struct file *, filldir_t, void *);
 extern int iterate_dir(struct file *, struct dir_context *);
 
 extern int vfs_stat(const char __user *, struct kstat *);