Fix clippy warnings (#1385)

## Issue Addressed

NA

## Proposed Changes

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

common/eth2_testnet_config/build.rs

@@ -1,6 +1,5 @@
 //! Downloads a testnet configuration from Github.
 
-use reqwest;
 use std::env;
 use std::fs::File;
 use std::io::Write;