Re-enable the blockhash test for constantinople.

[ekpyron]

Came up in #4799.

For constantinople the blockhash opcode seems to always return zero.
This is probably due to us setting the constantinople fork block to zero and resetting the chain to block zero before each test, which seems to break the blockchain contract in aleth (introduced in EIP96). Either our test setup has to be adjusted or aleth should support blockhash in the configuration used for our tests.

Corresponding issue in aleth: ethereum/aleth#5184

[ekpyron]

Pre-deploying the blockhash contract by adding it to the pre-defined accounts during genesis in RPCSession.cpp seems to help, but causes issues with other tests (https://circleci.com/gh/ethereum/solidity/30991).

[chriseth]

@ekpyron is this still the case?

[ekpyron]

It's not the case anymore, no, but the blockhash is still disabled for "< constantinople". Since we require newer aleth versions now anyways, we should reenable it. I'll rename this and create a suitable PR that closes this then.

[chriseth]

I believe this has been done in #6145

[ekpyron]

Confirmed: this was done in #6145.