chore(vc): remove the p2p client validator callback

[Maddiaa0]

Overview

In https://github.com/AztecProtocol/aztec-packages/pull/7854, where the validator client a code organisation issue is bandaided by having the p2p client call back into the validator client whenever it receives a proposal ( in order to perform an attestation ).

This callback method makes me uncomfortable and feels like an anti pattern. The AC of this issue is to reorganise the code to remove this callback pattern.