* chore: remove unused test helper from sqlstore
TimeNow() is no longer used in any tests in this package.
* chore: move sqlstore.SQLBuilder to the infra/db package
This required some minor refactoring; we need to be a little more explicit about passing around the dialect and engine. On the other hand, that's a few fewer uses of the `dialect` global constant!
* chore: move UserDeletions into the only package using it
* cleanup around moving sqlbuilder
* remove dialect and sqlog global vars
* rename userDeletions to serviceAccountDeletions
