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_types/src/fixed_vector.rs

@@ -364,7 +364,7 @@ mod test {
     fn ssz_round_trip<T: Encode + Decode + std::fmt::Debug + PartialEq>(item: T) {
         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));
     }
 
     #[test]

consensus/ssz_types/src/variable_list.rs

@@ -345,7 +345,7 @@ mod test {
     fn round_trip<T: Encode + Decode + std::fmt::Debug + PartialEq>(item: T) {
         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));
     }
 
     #[test]