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/eth2_libp2p/tests/common/mod.rs

@@ -142,7 +142,7 @@ pub async fn build_full_mesh(
     }
     let multiaddrs: Vec<Multiaddr> = nodes
         .iter()
-        .map(|x| get_enr(&x).multiaddr()[1].clone())
+        .map(|x| get_enr(x).multiaddr()[1].clone())
         .collect();
 
     for (i, node) in nodes.iter_mut().enumerate().take(n) {
@@ -216,7 +216,7 @@ pub async fn build_linear(rt: Weak<Runtime>, log: slog::Logger, n: usize) -> Vec
 
     let multiaddrs: Vec<Multiaddr> = nodes
         .iter()
-        .map(|x| get_enr(&x).multiaddr()[1].clone())
+        .map(|x| get_enr(x).multiaddr()[1].clone())
         .collect();
     for i in 0..n - 1 {
         match libp2p::Swarm::dial_addr(&mut nodes[i].swarm, multiaddrs[i + 1].clone()) {