Modlog API should have some cleanup of case types

[TrustyJAID]

Feature request

Modlog API should have some cleanup of case types.

Select the type of feature you are requesting:

• Cog
• Command
• API functionality

Describe your requested feature

As a bot owner, sometimes a new cog comes around that might be better suited to perform a task. If a cog currently decides to use the Modlog API and register a case type that is now set in the bot indefinitely. I may never want to utilize that modlog case again. Furthermore it can be confusing seeing a set of cases for a cog that is not currently present on the bot.