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>

common/monitoring_api/src/lib.rs

@@ -131,8 +131,8 @@ impl MonitoringHttpClient {
         let freezer_db_path = self.db_path.as_ref().ok_or_else(|| {
             Error::BeaconMetricsFailed("Beacon metrics require freezer db path".to_string())
         })?;
-        let metrics = gather_beacon_metrics(&db_path, &freezer_db_path)
-            .map_err(Error::BeaconMetricsFailed)?;
+        let metrics =
+            gather_beacon_metrics(db_path, freezer_db_path).map_err(Error::BeaconMetricsFailed)?;
         Ok(MonitoringMetrics {
             metadata: Metadata::new(ProcessType::BeaconNode),
             process_metrics: Process::Beacon(metrics),