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>

validator_client/src/lib.rs

@@ -84,7 +84,7 @@ impl<T: EthSpec> ProductionValidatorClient<T> {
         context: RuntimeContext<T>,
         cli_args: &ArgMatches<'_>,
     ) -> Result<Self, String> {
-        let config = Config::from_cli(&cli_args, context.log())
+        let config = Config::from_cli(cli_args, context.log())
             .map_err(|e| format!("Unable to initialize config: {}", e))?;
         Self::new(context, config).await
     }