v20250630-164255

runners: Revert things related to batch termination (#6868)

This reverts the following PRs:
* #6859 
* #6858 
* #6855 
* #6854
* #6852

These were causing issues where scale-down was too aggressively scaling
down instances leading to runners not being refreshed by scale-up.

I do think the SSM expiration stuff is worth a re-do though but there
were merge conflicts so I have to revert the entire thing.