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• finalizer_policy.cpp only exists for the following reason, which is no longer applicable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

Resolved #2044

[greg7mdp]

~~I seem to remember that @heifner had created this on purpose to avoid including the bls12 headers somewhere (was it contracts?). ~~
OK, just saw the comment I missed.

[ericpassmore]

Note:start
group: IF
category: CHORE
summary: Consolidation and refactoring created some un-needed files. This PR removed those un-needed files.
Note:end