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>

consensus/ssz/tests/tests.rs

@@ -9,7 +9,7 @@ mod round_trip {
         for item in items {
             let encoded = &item.as_ssz_bytes();
             assert_eq!(item.ssz_bytes_len(), encoded.len());
-            assert_eq!(T::from_ssz_bytes(&encoded), Ok(item));
+            assert_eq!(T::from_ssz_bytes(encoded), Ok(item));
         }
     }