Cleanup IntervalList orphans in nightly job only

[samuelbray32]

Description

Fixes #1194 (solution 2)

• remove IntervalList cleanup from Mixin.delete()
• Add IntervalList.cleanup() to documentation for nightly cron job

Checklist:

• N This PR should be accompanied by a release: (yes/no/unsure)
• NA If release, I have updated the CITATION.cff
• N This PR makes edits to table definitions: (yes/no)
• NA If table edits, I have included an alter snippet for release notes.
• NA If this PR makes changes to position, I ran the relevant tests locally.
• I have updated the CHANGELOG.md with PR number and description.
• NA I have added/edited docs/notebooks to reflect the changes

[CBroz1]

One small note, but this looks good. Have you already edited the corresponding chron job script? I would want to make sure that's updated in tandem with this merge

[edeno]

Based on lab meeting discussion, should we move this to a weekly job?

[CBroz1]

Based on lab meeting discussion, should we move this to a weekly job?

I think so. We could rename all nightly_cleanup to just cleanup, and set up a separate cron job for IntervalList.cleanup()