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>

lcli/src/generate_bootnode_enr.rs

@@ -47,7 +47,7 @@ pub fn run<T: EthSpec>(matches: &ArgMatches) -> Result<(), String> {
     let mut enr_file = File::create(output_dir.join(ENR_FILENAME))
         .map_err(|e| format!("Unable to create {}: {:?}", ENR_FILENAME, e))?;
     enr_file
-        .write_all(&enr.to_base64().as_bytes())
+        .write_all(enr.to_base64().as_bytes())
         .map_err(|e| format!("Unable to write ENR to {}: {:?}", ENR_FILENAME, e))?;
 
     let secret_bytes = match local_keypair {