Summary:
Depends on D21018. Ref T13493. Ref T6703. The "ExternalAccount" table has a unique key on `<accountType, accountDomain, accountID>` but this no longer matches our model of reality and changes in this sequence end writes to `accountID`.
Remove this key.
Then, remove all readers of `accountType` and `accountDomain` (and all nontrivial writers) because none of these callsites are well-aligned with plans in T6703.
This change has no user-facing impact today: all the rules about linking/unlinking/etc remain unchanged, because other rules currently prevent creation of more than one provider with a given "accountType".
Test Plan:
- Linked an OAuth1 account (JIRA).
- Linked an OAuth2 account (Asana).
- Used `bin/auth refresh` to cycle OAuth tokens.
- Grepped for affected symbols.
- Published an Asana update.
- Published a JIRA link.
Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam
Maniphest Tasks: T13493, T6703
Differential Revision: https://secure.phabricator.com/D21019
