Move SKU-specific events from EntitlementObserver to Handlers, cleanup useless code

Summary: Handlers are a better location for this code. Bumping entitleable->updated_at was useless.

Test Plan: ./phpunit

Reviewers: #hkccp_developers, mollekopf

Reviewed By: #hkccp_developers, mollekopf

Subscribers: #hkccp_developers

Differential Revision: https://git.kolab.org/D4607