Remove deal_ids field from SectorOnChainInfo

[anorth]

From FIP-0076, the sector deal_ids field is deprecated. We left it in place to preserve the data in all the existing sectors, where it might be useful for some disaster recovery in case the migration is broken, etc. But once the network is operating smoothly without using it, we can delete the field next time we migrate sector info.

[kamuik16]

Hey @anorth @rjan90
I can work on this if you guys have decided to remove the field. Lmk.

[Stebalien]

we can delete the field next time we migrate sector info.

As far as I know, we have no FIPs planned that need to re-write the sector infos. We won't remove this field until then as that would lead to a lot of unnecessary state churn.