configfs_register_group() shouldn't be (and isn't) called in rmdirable parts

revert cc57c073 "configfs: fix registered group removal"
It was an attempt to handle something that fundamentally doesn't
work - configfs_register_group() should never be done in a part
of tree that can be rmdir'ed.  And in mainline it never had been,
so let's not borrow trouble; the fix was racy anyway, it would take
a lot more to make that work and desired semantics is not clear.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@lst.de>

fs/configfs/dir.c

@@ -1771,16 +1771,6 @@ void configfs_unregister_group(struct config_group *group)
 	struct dentry *dentry = group->cg_item.ci_dentry;
 	struct dentry *parent = group->cg_item.ci_parent->ci_dentry;
 
-	mutex_lock(&subsys->su_mutex);
-	if (!group->cg_item.ci_parent->ci_group) {
-		/*
-		 * The parent has already been unlinked and detached
-		 * due to a rmdir.
-		 */
-		goto unlink_group;
-	}
-	mutex_unlock(&subsys->su_mutex);
-
 	inode_lock_nested(d_inode(parent), I_MUTEX_PARENT);
 	spin_lock(&configfs_dirent_lock);
 	configfs_detach_prep(dentry, NULL);
@@ -1796,7 +1786,6 @@ void configfs_unregister_group(struct config_group *group)
 	dput(dentry);
 
 	mutex_lock(&subsys->su_mutex);
-unlink_group:
 	unlink_group(group);
 	mutex_unlock(&subsys->su_mutex);
 }