Remove 10-block rolling finalization

Summary:
Now that Avalanche is enabled by default the 10-block rolling finalization is safe to remove.

Removing this now will make adding Avalanche block policies easier and lower risk.

Depends on D13063

Test Plan:

ninja check check-functional

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13058