simplify how EVM config is defined as a ledger parameter

chain-impl-mockchain/src/config.rs

@@ -14,7 +14,7 @@ use chain_core::packer::Codec;
 use chain_core::property;
 use chain_crypto::PublicKey;
 #[cfg(feature = "evm")]
-use chain_evm::machine::{BlockCoinBase, BlockHash, Config, Environment, Origin};
+use chain_evm::machine::{BlockCoinBase, BlockHash, Environment, Origin};
 #[cfg(feature = "evm")]
 use std::convert::TryInto;
 use std::{
@@ -848,13 +848,6 @@ impl ConfigParamVariant for EvmConfigParams {
     }
 
     fn from_payload(payload: &[u8]) -> Result<Self, Error> {
-        fn check_bool(b: u8) -> Result<bool, Error> {
-            match b {
-                0 => Ok(false),
-                1 => Ok(true),
-                _ => Err(Error::BoolInvalid),
-            }
-        }
         let mut rb = ReadBuf::from(payload);
 
         // Read EvmConfig and match hard fork variant