Type of PR:

• Other

Required reviews:

• 3

What this does:
Removes IndisputableEvidence, utilities that were only used in it, and tests that check it.

Why it's needed:
Currently IndisputableEvidence can only lead to the slashing of an Ursula if she signs an incorrect cfrag and sends it to Bob. A minimally competent malicious Ursula won't expose herself that way, so it is not particularly useful.

Additionally, it is discarded after creation in the current codebase - it is not even sent out if the cfrag is invalid.

As discussed on a meeting, we remove IndisputableEvidence (to help with the adoption of the new Umbral), but keep the Adjudicator contract for now because of additional actions required to change the deployment process. But eventually it needs to be updated to do something useful. See #305.

List of changes:

• removed IndisputableEvidence
• removed recover_pubkey_from_signature
• removed nucypher.types.Evidence
• Bob._reencrypt() returns a list of offender Ursulas on failure instead of list of evidences
• removed slashing sections from estimate_gas.py
• _mock_ursula_reencrypts() returns a PRETask instead of IndisputableEvidence, and does not accept a corrupt_cfrag kwarg
• removed test_slashing() from test_intercontract_integration.py (note that I had to add the commitments from this tests to the next one, test_withdraw()). There's already a slashing test for StakingEscrow.
• removed get_coordinates_as_bytes() and simplified canonical_address_from_umbral_key()
• moved get_signature_recovery_value() to the only test where it is used.
• removed tests:
  • tests/acceptance/blockchain/actors/test_investigator.py
  • tests/acceptance/blockchain/agents/test_adjudicator_agent.py
  • tests/contracts/lib/test_reencryption_validator.py
  • tests/contracts/main/adjudicator (whole folder)
  • tests/unit/crypto/test_coordinates_serialization.py
  • tests/unit/crypto/test_umbral_signatures.py

Note that I kept AdjudicatorAgent in place for now, because it seems to be used in deployment.