Estimated rewards for anchors use post-AMK logic

[Bushstar]

Summary

• GetAnchorSubsidy has not been used since the AMK fork, since then the anchor reward has been whatever has accumulated in the Anchor Reward Community Balance. This PR updates the estimated rewards to use the community balance.

Implications

• Storage

  • [ ] Database reindex required
  • [ ] Database reindex optional
  • [ ] Database reindex not required
  • [x] None

• Consensus

  • [ ] Network upgrade required
  • [ ] Includes backward compatible changes
  • [ ] Includes consensus workarounds
  • [ ] Includes consensus refactors
  • [x] None