[avalanche] Always send an avahello message if we have a proof
This diff removes the filter so we can send avahello messages to peers that don't set the avalanche service bit. This has several benefits:
- It is less code and less edge cases. Peers with avalanche disabled will simply ignore the message.
- It makes it possible for a node with avalanche turned on but no proof to poll the network (but it will not be polled, it's kind of a read only mode).
- It removes the need to broadcast our local proof entirely, leading to further simplification, because sending an avahello is equivalent to sending an inv with our proofid.
ninja all check-all
Reviewers: #bitcoin_abc, tyler-smith
Reviewed By: #bitcoin_abc, tyler-smith
Differential Revision: https://reviews.bitcoinabc.org/D11365