Remove a very old Herald garbage collection migration

Summary:
Ref T13048. This migration is from January 2012 and probably only impacted Facebook.

It references HeraldRepetitionPolicyConfig, which I'd like to change significantly. I initially just replaced the constant with a literal 0, but I don't think there's any actual value in retaining this migration nowadays.

The cost of removing this migration is: if you installed Phabricator before January 2012 and haven't upgraded since then, you'll have a few more rows in the APPLIED table than necessary. Herald will still work correctly.

Test Plan: Reading.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13048

Differential Revision: https://secure.phabricator.com/D18924