Fix clippy warnings (#1385)

## Issue Addressed

NA

## Proposed Changes

Fixes most clippy warnings and ignores the rest of them, see issue #1388.

beacon_node/eth2_libp2p/src/rpc/methods.rs

@@ -182,7 +182,7 @@ impl ssz::Decode for GoodbyeReason {
     }
 
     fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, ssz::DecodeError> {
-        u64::from_ssz_bytes(bytes).and_then(|n| Ok(n.into()))
+        u64::from_ssz_bytes(bytes).map(|n| n.into())
     }
 }