Fix test helpers to not depend on leaked execution data

[potuz]

The current beacon state contains unnecessary information about the execution layer state. See for example #3612

This information is nowhere used in the consensus layer, yet the testsuite assume it is there in many places. The generators for empty execution payloads for example take only a beacon state as argument, and gather the latest state root of the execution layer from it.

The testsuite should be refactor so that the caller of these helpers passes the execution layer data and should not assume that a beacon state will forever hold this leaked information.