Fix reconcile_messages() regression to only reconcile with local Inbox-created messages.

Summary:
Filtering by the inbox-uid header alone is not sufficient; more than one
message on the remote backend may have the same inbox-uid header.
Reconciliation should only occur with messages created locally, not messages synced;
that is incorrect and also causes issues like T550.

Test Plan: Regression test in inbox-eas.

Reviewers: emfree

Reviewed By: emfree

Differential Revision: https://review.inboxapp.com/D596