Rust 1.54.0 lints (#2483)

## Issue Addressed

N/A

## Proposed Changes

- Removing a bunch of unnecessary references
- Updated `Error::VariantError` to `Error::Variant`
- There were additional enum variant lints that I ignored, because I thought our variant names were fine
- removed `MonitoredValidator`'s `pubkey` field, because I couldn't find it used anywhere. It looks like we just use the string version of the pubkey (the `id` field) if there is no index

## Additional Info



Co-authored-by: realbigsean <seananderson33@gmail.com>

beacon_node/src/config.rs

@@ -264,7 +264,7 @@ pub fn get_config<E: EthSpec>(
     /*
      * Load the eth2 network dir to obtain some additional config values.
      */
-    let eth2_network_config = get_eth2_network_config(&cli_args)?;
+    let eth2_network_config = get_eth2_network_config(cli_args)?;
 
     client_config.eth1.deposit_contract_address = format!("{:?}", spec.deposit_contract_address);
     client_config.eth1.deposit_contract_deploy_block =