Reduce two queries in updateExpiredBells() down to one

What does this MR do?

See title

How confident are you it won't break things if deployed?

Very

Links to related issues

• Idea came from here: https://yunity.slack.com/archives/C1T1ZM9A4/p1574718916326800

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• joined #foodsharing-beta channel at https://slackin.yunity.org
• [?] added an entry to CHANGELOG.md (description, merge request link, username(s))
• Once your MR has been merged, you are responsible to update the #foodsharing-beta Slack channel about what has been changed here. They will test your work in different browsers, roles or other settings