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/store/src/hot_cold_store.rs

@@ -305,7 +305,7 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> HotColdDB<E, Hot, Cold>
     pub fn put_state(&self, state_root: &Hash256, state: &BeaconState<E>) -> Result<(), Error> {
         let mut ops: Vec<KeyValueStoreOp> = Vec::new();
         if state.slot() < self.get_split_slot() {
-            self.store_cold_state(state_root, &state, &mut ops)?;
+            self.store_cold_state(state_root, state, &mut ops)?;
             self.cold_db.do_atomically(ops)
         } else {
             self.store_hot_state(state_root, state, &mut ops)?;
@@ -563,7 +563,7 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> HotColdDB<E, Hot, Cold>
                 "slot" => state.slot().as_u64(),
                 "state_root" => format!("{:?}", state_root)
             );
-            store_full_state(state_root, &state, ops)?;
+            store_full_state(state_root, state, ops)?;
         }
 
         // Store a summary of the state.
@@ -861,7 +861,7 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> HotColdDB<E, Hot, Cold>
 
             per_block_processing(
                 &mut state,
-                &block,
+                block,
                 None,
                 BlockSignatureStrategy::NoVerification,
                 &self.spec,

beacon_node/store/src/lib.rs

@@ -271,7 +271,7 @@ mod tests {
     fn simplediskdb() {
         let dir = tempdir().unwrap();
         let path = dir.path();
-        let store = LevelDB::open(&path).unwrap();
+        let store = LevelDB::open(path).unwrap();
 
         test_impl(store);
     }