Revert "Allow starting networks from arbitrary actor versions"

[magik6k]

Reverts #6305 - It seems to break devnets

Getting this when starting the genesis miner:

2021-05-26T11:03:15.011+0100    ERROR   main    lotus-storage-miner/init.go:259 Failed to initialize lotus-miner: failed to configure miner:
    main.storageMinerInit
        /home/mvdan/git/lotus/cmd/lotus-storage-miner/init.go:490
  - GasEstimateMessageGas error: estimating gas used: message execution failed: exit SysErrorIllegalActor(9), reason: unsupported actor: actor bafkqaetgnfwc6mjpon2g64tbm5sw22lomvza is a version 0 actor; chain only supports actor version 4 at height 1 and nver 12 (RetCode=9)

[mvdan]

Thanks! This fixes how we start lotus daemon + miner for dealbot integration tests in https://github.com/filecoin-project/dealbot/tree/main/devnet.