[Network] PeerDB should enforce at most one row per public key hash

[jcnelson]

Due to node churn, especially in NAT'ed automated clusters, it's possible that the same peer can be represented in multiple rows while having the same public key. Unfortunately, this isn't as simple as declaring the public key to be the primary key due to the way the PeerDB is structured.

[blockstack-devops]

This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.