Merge #2704

2704: Shelley: only keep a compact genesis config in memory r=mrBliss a=mrBliss

Some fields in the Shelley genesis config are only needed at start-up. There's
no point in keeping them in memory during the rest of the execution. In some
testing setups, e.g., for transaction benchmarking, the genesis config can be
quite large.

This also means that the `GetGenesisConfig` query (#2694) would only return the
compact genesis config, not the original full one.

Co-authored-by: Thomas Winant <[email protected]>

Author: iohk-bors[bot]