Fix clippy errors on tests (#2160)

## Issue Addressed

There are some clippy error on tests.


## Proposed Changes

Enable clippy check on tests and fix the errors. 💪

consensus/int_to_bytes/src/lib.rs

@@ -78,7 +78,6 @@ pub fn int_to_bytes96(int: u64) -> Vec<u8> {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use hex;
     use std::{fs::File, io::prelude::*, path::PathBuf};
     use yaml_rust::yaml;