[ecash-herald] Stop handling block connected event

Summary: Now that we build more helpful messages for blocks that are invalidated by avalanche, stop "guessing" that blocks have a problem if they are connected by not finalized after an arbitrary amount of time.

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D16906