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>

boot_node/src/config.rs

@@ -29,7 +29,7 @@ impl<T: EthSpec> TryFrom<&ArgMatches<'_>> for BootNodeConfig<T> {
         let data_dir = get_data_dir(matches);
 
         // Try and grab network config from input CLI params
-        let eth2_network_config = get_eth2_network_config(&matches)?;
+        let eth2_network_config = get_eth2_network_config(matches)?;
 
         // Try and obtain bootnodes