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>

testing/ef_tests/src/cases/rewards.rs

@@ -53,7 +53,7 @@ type Accessor = fn(&AttestationDelta) -> Δ
 
 fn load_optional_deltas_file(path: &Path) -> Result<Option<Deltas>, Error> {
     let deltas = if path.is_file() {
-        Some(ssz_decode_file(&path)?)
+        Some(ssz_decode_file(path)?)
     } else {
         None
     };