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/validator_dir/src/builder.rs

@@ -180,7 +180,7 @@ impl<'a> Builder<'a> {
                     signature: Signature::empty().into(),
                 };
 
-                deposit_data.signature = deposit_data.create_signature(&voting_keypair.sk, &spec);
+                deposit_data.signature = deposit_data.create_signature(&voting_keypair.sk, spec);
 
                 let deposit_data =
                     encode_eth1_tx_data(&deposit_data).map_err(Error::UnableToEncodeDeposit)?;