Remove known-drift callouts from new_repo_checklist

[Christdej]

Removes the four Known drift callouts and the bottom-of-file "Notes" reference to them. These were a snapshot in time of the state during the initial audit; drift will be remediated (see the follow-up rollout using ~/scripts/audit_repos.sh) and re-stating it in the checklist would go stale.

Removed:

• §2 branch ruleset — bullets naming sara-utilities, sara-stid, sara-anonymizer.
• §4 environments — sentence about most sara repos having zero environments; kept the "all three or none, keep consistent" guidance as it's still a policy statement rather than drift.
• §5 secrets — sentence about obsolete ROBOTICS_AURORA* secrets and the delete example.
• Notes section — bullet pointing to "Known drift callouts".

The checklist is now purely prescriptive.