Clean up power actor MinerAboveMinPowerCount state for miners with invalid sector sizes #1423
Description
In #1345 we unintentionally lost a check that prevented creation of new miners with proofs types that are not supported by the network. A few miners with unsupported sector sizes were created on mainnet. These miners can never commit a sector so are essentially DOA. However, the 2KiB miners incremented st.MinerAboveMinPowerCount because the consensus minimum power for that sector size is zero.
This is not a practical problem for mainnet, but it would still be good to clean up the state to properly reflect that these miners are ineligible to produce a block. It's a logical flaw to count zero-powered miners towards the ConsensusMinerMinMiners threshold. I might suggest removing their claims from the power table might be a good way to do it (and updating the MinerAboveMinPowerCount to be consistent). But other approaches might work too.
See also #1421