Remove separate carbonOffsetPartner tracking

[palango]

It seems that CarbonOffsetPartnerStartOf is not actively used.

I'm a bit surprised by that and want to run more testing on this.

• Investigate epoch rewards calculation in respect to LockedGold and sub-accounts

[eelanagaraj]

Notes about removing this

After looking into this, we confirmed that these rewards are already covered by Rosetta (i.e. doesn’t look like we need to fix a bug/exclude addresses from reconciliation), therefore it's fine to remove the (unused) carbonOffset stuff in Rosetta without needing to add any additional logic to cover epoch rewards calculations.

Details:

• carbonOffsetPartner is still relevant post-Gingerbread — this is the portion of epoch rewards that is used for offsetting
  • according to CIP-52, eventually this will be redirected to the Green Fund (but simply by setting the carbonOffsettingPartner in EpochRewards.sol to point to this)
• Ultragreen adds offsetting of a portion of the base fee (20% goes to the new Green Fund, 80% burned)
  blockchain code (in distributeEpochRewards) uses the Mint function (in GoldToken.sol) which emits a Transfer event
  • Rosetta simply filters on all transfers made in the last tx of the block (i.e. epoch reward tx), which should thus already include the carbon offsetting portion of epoch rewards

Tested

Ran reconciliation checks locally on mainnet past epoch 10 (contains epoch rewards paid out to the carbon offsetting partner 0x0ba9f5b3cdd349ab65a8dacda9a38bc525c2e6d6) + marking that account as an interesting account to ensure the balances were reconciled.

[eelanagaraj]

rebased master, confirmed that this logic is already covered