Fix an issue with destruction of Revision and Diff objects with viewstates

Summary:
See https://discourse.phabricator-community.org/t/domainexception-when-trying-to-remove-an-differentialrevision/4105.

These queries aren't actually constructed properly, and destroying a revision or diff with viewstates currently fails.

Test Plan: Used bin/remove destroy Dxxx to destroy a revision with viewstates (this also destroys the associated diffs).

Differential Revision: https://secure.phabricator.com/D21421