Clear inactive assignee for old high-priority bugs without needinfo

[benjaminmah]

Resolves #1759.

Depends on #2515 to remove the TypeError.

Checklist

• [ ] Type annotations added to new functions
• [ ] Docs added to functions touched in main classes
• [ ] Dry-run produced the expected results
• [ ] The to-be-announced tag added if this is worth announcing

[suhaibmujahid]

Could you please rebase?