Reset certain columns in eas keep_tables

Summary:
With just ./tools/clear-db (i.e. --with users not specified), we want to keep the easaccount table but reset
eas_account_sync_key=0 (i.e. get rid of all sync state info)

See matching push to inbox-util

Test Plan: Expected effect for both gmail, EAS.

Reviewers: spang

Differential Revision: https://review.inboxapp.com/D60
default->server_default in database tables