Cleanup blockchain + state VM test runner

[jochem-brouwer]

verifyPostConditions in VM does not seem to work (it has bugs, such as stripHexPrefix and then trying to hexToBytes, which fails because it is not 0x-prefixed). Also, the Blockchain test runner passes a root argument, but this does not seem necessary.

In general, clean up the Blockchain and State test runners by removing all logic which is not necessary to run the tests, and ensure that the utility helper functions work.