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/state_processing/src/upgrade/altair.rs

@@ -26,7 +26,7 @@ pub fn translate_participation<E: EthSpec>(
         // Apply flags to all attesting validators.
         let committee = state.get_beacon_committee(data.slot, data.index)?;
         let attesting_indices =
-            get_attesting_indices::<E>(&committee.committee, &attestation.aggregation_bits)?;
+            get_attesting_indices::<E>(committee.committee, &attestation.aggregation_bits)?;
         let epoch_participation = state.previous_epoch_participation_mut()?;
 
         for index in attesting_indices {