Remove vesting from PreCommitSector and ConfirmSectorProofsValid

[anorth]

Background
Vesting is processed via State.UnlockVestedFunds, which is called from PreCommitSector, ConfirmSectorProofsValid, WithDrawBalance and the deadline cron. The original motivation for computing vesting on sector commitment is so that any vested funds could be used for pre-commit deposit or pledge.

The vesting table is quantized to 12-hr increments. Since vesting is processed in the deadline cron every 30 minutes, the calls during sector commitment almost always achieve nothing. The most it could achieve is to accelerate a release by 30 minutes.

Processing reward vesting is quite expensive as it loads and stores a sizeable array for the vesting table. For high-scale miners, committing many sectors per deadline (or even per-epoch), this represents a sizeable portion of total gas cost and chain bandwidth consumption.

Proposal
Remove vesting from PreCommitSector and ConfirmSectorProofsValid, leaving it to the deadline cron. If necessary, the miner's owner can trigger vesting via WithdrawBalance (possibly with an argument of zero).

This will reduce the gas consumption of these methods substantially, freeing up chain bandwidth for other messages, reducing gas costs, and/or improving validation speed.

First proposed in filecoin-project/specs-actors#1258

[momack2]

More chain throughput (via lower gas usage) sounds great! The slight delay in miner rewards (which can be solved by manually triggering WithdrawBalance seems like a reasonable cost for such an improvement. 👍

[anorth]

Closed by #19

[momack2]

Keeping this open as a place for discussion on FIP-0005

[nicola]

I think this can be closed now that it's accepted, correct? https://github.com/filecoin-project/FIPs/blob/master/FIPS/fip-0005.md