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>

validator_client/src/notifier.rs

@@ -20,7 +20,7 @@ pub fn spawn_notifier<T: EthSpec>(client: &ProductionValidatorClient<T>) -> Resu
         loop {
             if let Some(duration_to_next_slot) = duties_service.slot_clock.duration_to_next_slot() {
                 sleep(duration_to_next_slot + slot_duration / 2).await;
-                notify(&duties_service, &log).await;
+                notify(&duties_service, log).await;
             } else {
                 error!(log, "Failed to read slot clock");
                 // If we can't read the slot clock, just wait another slot.