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/gather.rs

@@ -153,7 +153,7 @@ pub fn gather_metrics(metrics_map: &HashMap<String, JsonMetric>) -> Option<serde
     for mf in metric_families.iter() {
         let metric_name = mf.get_name();
         if metrics_map.contains_key(metric_name) {
-            let value = get_value(&mf).unwrap_or_default();
+            let value = get_value(mf).unwrap_or_default();
             let metric = metrics_map.get(metric_name)?;
             let value = metric.get_typed_value(value);
             let _ = res.insert(metric.json_output_key.to_string(), value);