Fixes T4636. If a user manually deletes a "repository" setting from a revision, Herald attempts to resolve it. Instead, Herald should now just trust Differential. Generally, the new logic is:

• When diffs are created, figure out repository information.
• When revisions are updated, copy info from diffs.
• Everywhere else, just trust the revision field.

• Created revisions.
• Used Herald to dry-run revisions before and after a manual edit to remove the repository setting.