(Later...) Drop legacy Project transaction table

Summary: Ref T4010. I'll hold this for a bit, but we should eventually drop this table once the dust has settled.

Test Plan: Ran storage upgrade.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4010

Differential Revision: https://secure.phabricator.com/D7372