R1:562da7e98bf0

Stop using loadRelationships in differential related herald adapters

Summary:
Used `DifferentialRevisionQuery` with the relevant `need*()` calls in the test controller.
And started assuming the revision has reviewers and CC phids in `HeraldDifferentialRevisionAdapter`.

Test Plan:
Added herald rules that use revisions (one for revisions another for commit) and reviewers.
Created, accepted and landed a revision that matched the rules and checked all rules were applied.

Reviewers: epriestley

Reviewed By…