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>

beacon_node/beacon_chain/src/naive_aggregation_pool.rs

@@ -574,7 +574,7 @@ mod tests {
     }
 
     fn key_from_sync_contribution(a: &SyncCommitteeContribution<E>) -> SyncContributionData {
-        SyncContributionData::from_contribution(&a)
+        SyncContributionData::from_contribution(a)
     }
 
     macro_rules! test_suite {