Issue: Cannot delete discussion topics

Some discussion topics are added via the Admin Panel, so they must be deleted the same way. Under Presets > Discussion Topics, click the X next to the topic to delete it completely. To remove it only from certain areas, edit the area in question and change the setting "Discussion Topics Allowed in this Area".

For user-created discussions, I see that indeed the moderator tools drop-down is missing on the discussion list. Fixed in the next release.

Was this fix pushed to RC2 or a later version? Because I still do not see it in RC1

You must be in the discussion list view that shows only a list of the open discussions. (?do=comments&action=list)
You typically access this view by clicking the "View All Discussions" button below the discussions preview box on a page when there are more discussions than that preview can show.

There are no moderator controls on the previews for any kind of content. If that is what you mean, then that would be a feature request since it would require code changes to the way the previews are currently made.

Example: https://www.vaultwiki.org/pages/
The 'Discussions for Wiki' box is just a cached preview of some discussions that 'Wiki' has. If you click 'View All Discussions' you access the real discussion list where the moderator controls are.