4.7: Remove scripts for moderation tables

Comment moderation was removed from core in 4.7. Other projects are moving in to fill the void (like drumm's karma module), but we still create the unused moderation_filters, moderation_roles, and moderation_votes tables.

Attached is a patch that removes those tables from the db creation script. We do NOT want to delete the tables in the update, because important data will be stored there for those who were using the moderation system. Preserving the existing table data will allow new modules to provide a migration path.