R1:7e8dc0742bdc

Remove all callers to "DifferentialRevision->loadIDsByCommitPHIDs()"

Summary: Depends on D20457. Ref T13276. Kill all remaining callers to this method and delete it.

Test Plan:
- Grepped for `loadIDsByCommitPHIDs`.
- Viewed blame again to make sure I didn't break it.
- Viewed "History" view for commits with revisions.
- Viewed "Graph" view for commits with revisions.
- Viewed "Merged Commits" table for commits with revisions.
- Viewed "Compare" table for commits with revisions.
- Viewed "Repository" main…