[SCHEMA] Fix nullable constraints on EASUid and EASFoldersync state enum.

Summary:
The former we tightened on Gmail at one point and didn't trickle it back
to EAS. The latter is a bug from way back.

We really need to figure out a better deal for what to do with EAS-only
migrations, but putting it here for now.

Depends on D153

Test Plan: Upgrade/downgrade.

Reviewers: kav-ya

Reviewed By: kav-ya

Differential Revision: https://review.inboxapp.com/D154