vfs: push dentry_unhash on rmdir into file systems

Only a few file systems need this.  Start by pushing it down into each
fs rmdir method (except gfs2 and xfs) so it can be dealt with on a per-fs
basis.

This does not change behavior for any in-tree file systems.

Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/ubifs/dir.c

@@ -656,6 +656,8 @@ static int ubifs_rmdir(struct inode *dir, struct dentry *dentry)
 	struct ubifs_inode *dir_ui = ubifs_inode(dir);
 	struct ubifs_budget_req req = { .mod_dent = 1, .dirtied_ino = 2 };
 
+	dentry_unhash(dentry);
+
 	/*
 	 * Budget request settings: deletion direntry, deletion inode and
 	 * changing the parent inode. If budgeting fails, go ahead anyway