Subscriptions and Moderators have no sense for a Category

[casiepa]

A forum can have subscriptions and can be moderated, but when it's a category there seems to be little sense to subscribe to it or moderate.

So the 'Subscriptions' and the 'Moderators' meta box could be removed/hidden when editing a forum of type category

[netweb]

For moderation, yes, I don't think we need the 'Forum Moderators" meta box though, it serves no purpose for categories.

IFor subscriptions I think there are use cases for subscribing to categories:

My IT Forum:

• Apple Operating Systems Category

-- iOS
--- iOS 10
--- iOS 9
-- macOS

• Windows

-- Windows 10
-- Windows 9

For the not great example above, I might want to subscribe to all the iOS forums of a category

Related: #2506 Add subscription to category or entire forum