Remove `is_stateless` flag

What is wrong?

There’s an is_stateless in VM configuration now: https://github.com/ethereum/py-evm/blob/4f476908dff42e290c15fc4cfb6a3c5e65e37dfe/evm/vm/base.py#L98-L127

In is_stateless mode, the block will be deeply copied and the get the result block from VMState with updated header and transactions. And in the non-stateless mode (the old route), the state transition result would be updated in VM.

How can it be fixed

1. Remove the is_stateless is False route.
2. Modify Chain.apply_transaction to update the local vm state before returning the computation object.

[pipermerriam]

I wonder what is the use case of Chain.apply_transaction(transaction) for full nodes or other scenarios?

For testing, full nodes, and mining are the use cases I can think of. It’s a mid/low level interface for building blocks incrementally.

[pipermerriam]

you pointed out that we should modify Chain.apply_transaction to update the local vm state before returning the computation object.

I think what I was referring to was that previously the Chain class’s state root would get updated automatically, but with the recent changes, that is no longer the case. So, the Chain object now needs to manually update the state root since it no longer happens automatically.