Remove the miner fund consensus code

Summary:
It is a block policy rule since wellington activated.

The code is changed so that it look like the consensus rules were never enforced as the past blocks are still valid. This also means we can remove the legacy IFP address related code.

Test Plan:

ninja all check-extended

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D14032