Use standard subscribers effects in Herald Adapter for commits

Summary: Ref T8455. Use the standard actions in commit rules, instead of a custom action.

Test Plan: Wrote an "add cc" Herald rule for commits, pushed a commit, saw the rule fire correctly.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8455

Differential Revision: https://secure.phabricator.com/D13181