This PR removes deprecated code:
- The `RuntimeGenesisConfig` generic type parameter in
`GenericChainSpec` struct.
- `ChainSpec::from_genesis` method allowing to create chain-spec using
closure providing runtime genesis struct
- `GenesisSource::Factory` variant together with no longer needed
`GenesisSource`'s generic parameter `G` (which was intended to be a
runtime genesis struct).


https://github.com/paritytech/polkadot-sdk/blob/17b56fae/substrate/client/chain-spec/src/chain_spec.rs#L559-L563