Prior to this change we were joining through `upstream_subscriptions`
and `downstream_subscriptions` relations to count `upstream_projects`
and `downstream_projects`. This uses the `ci_subscriptions_projects`
table. Since we've added `disable_joins` to these
`has_many ... through: ...` relations these queries will now be less
efficient. So instead we've simplified the query to not join at all as
the `ci_subscriptions_projects.upstream_project_id` and
`ci_subscriptions_projects.downstream_project_id` are already both
`NOT NULL` foreign keys which means we already know for sure that
counting the `ci_subscriptions_projects` rows is equivalent to counting
the `projects` rows.