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>

slasher/service/src/service.rs

@@ -214,7 +214,7 @@ impl<T: BeaconChainTypes> SlasherService<T> {
             // Publish to the network if broadcast is enabled.
             if slasher.config().broadcast {
                 if let Err(e) =
-                    Self::publish_attester_slashing(&beacon_chain, &network_sender, slashing)
+                    Self::publish_attester_slashing(beacon_chain, network_sender, slashing)
                 {
                     debug!(
                         log,
@@ -267,7 +267,7 @@ impl<T: BeaconChainTypes> SlasherService<T> {
 
             if slasher.config().broadcast {
                 if let Err(e) =
-                    Self::publish_proposer_slashing(&beacon_chain, &network_sender, slashing)
+                    Self::publish_proposer_slashing(beacon_chain, network_sender, slashing)
                 {
                     debug!(
                         log,

slasher/src/slasher.rs

@@ -244,7 +244,7 @@ impl<E: EthSpec> Slasher<E> {
             let slashing_status = self.db.check_and_update_attester_record(
                 txn,
                 validator_index,
-                &attestation,
+                attestation,
                 attester_record,
             )?;