LMS Rails 5.0 Prework - Address deprecation: passing string to define callback

[brendanshean]

WHAT

This PR addresses a Rails 5 deprecation for passing strings to define callbacks.

WHY

In order to upgrade to Rails 5 need to address deprecations

HOW

Update the after_commit blocks to use class method calls instead of strings.

Notion Card Links

https://www.notion.so/quill/Upgrade-LMS-to-Rails-5-0-b742cd5e1764427d8670944d50e2a3e3

PR Checklist	Your Answer
Have you added and/or updated tests?	No. There is no new functionality here, just a refactoring fo the upgrade.
Have you deployed to Staging?	Not yet - deploying now!
Self-Review: Have you done an initial self-review of the code below on Github?	YES
Design Review: If applicable, have you compared the coded design to the mockups?	Yes