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/eth1/src/inner.rs

@@ -48,7 +48,7 @@ impl Inner {
 
     /// Encode the eth1 block and deposit cache as bytes.
     pub fn as_bytes(&self) -> Vec<u8> {
-        let ssz_eth1_cache = SszEth1Cache::from_inner(&self);
+        let ssz_eth1_cache = SszEth1Cache::from_inner(self);
         ssz_eth1_cache.as_ssz_bytes()
     }