Don't require a valid proof for genesis blocks

[mrmr1993]

This PR skips the proof verification check for the genesis block when it's sent by another peer. Currently, nodes will send a dummy proof with the genesis block, and will then be banned by the receiving node.

Note that the node(s) that produce the first block will generate a genesis proof, which they will recursively verify in that block. It is never otherwise useful to generate and distribute a genesis proof, so we avoid doing so by removing this check.

This should fix some flakiness that we've been seeing in integration tests due to nodes banning eachother.

Checklist:

• Modified the current draft of release notes with details on what is completed or incomplete within this project
• Document code purpose, how to use it
  • Mention expected invariants, implicit constraints
• Tests were added for the new behavior
  • Document test purpose, significance of failures
  • Test names should reflect their purpose
• All tests pass (CI will check this if you didn't)
• Serialized types are in stable-versioned modules
• Does this close issues? List them