IF: remove unneeded files

[linh2931]

• finalizer_policy.cpp only exists for the following reason, which is no longer applicable

  /**
    * These definitions are all here to avoid including bls_public_key.hpp which includes <bls12-   381/bls12-381.hpp>
    * and pulls in bls12-381 types. This keeps bls12-381 out of libtester.
    */

• proposal_info.hpp was for proposal_info_extension which has been folded into instant_finality_extension.

Remove them from code base to have less cluters.