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. 💪

slasher/tests/attester_slashings.rs

@@ -107,7 +107,7 @@ fn surrounds_existing_single_val_single_chunk() {
 fn surrounds_existing_multi_vals_single_chunk() {
     let validators = vec![0, 16, 1024, 300_000, 300_001];
     let att1 = indexed_att(validators.clone(), 1, 2, 0);
-    let att2 = indexed_att(validators.clone(), 0, 3, 0);
+    let att2 = indexed_att(validators, 0, 3, 0);
     let slashings = hashset![att_slashing(&att2, &att1)];
     slasher_test_indiv(&[att1, att2], &slashings, 3);
 }

slasher/tests/proposer_slashings.rs

@@ -9,7 +9,7 @@ use types::{Epoch, EthSpec};
 fn empty_pruning() {
     let tempdir = tempdir().unwrap();
     let config = Config::new(tempdir.path().into());
-    let slasher = Slasher::<E>::open(config.clone(), logger()).unwrap();
+    let slasher = Slasher::<E>::open(config, logger()).unwrap();
     slasher.prune_database(Epoch::new(0)).unwrap();
 }
 

slasher/tests/random.rs

@@ -62,7 +62,7 @@ fn random_test(seed: u64, test_config: TestConfig) {
             .choose_multiple(&mut rng, num_attesters)
             .copied()
             .collect::<Vec<u64>>();
-        attesting_indices.sort();
+        attesting_indices.sort_unstable();
 
         // If checking slashings, generate valid attestations in range.
         let (source, target) = if check_slashings {

slasher/tests/wrap_around.rs

@@ -30,7 +30,7 @@ fn attestation_pruning_empty_wrap_around() {
 
     // Add an attestation that would be surrounded with the modulo considered
     slasher.accept_attestation(indexed_att(
-        v.clone(),
+        v,
         2 * history_length - 3,
         2 * history_length - 2,
         1,
@@ -48,7 +48,7 @@ fn pruning_with_map_full() {
     config.history_length = 1024;
     config.max_db_size_mbs = 1;
 
-    let slasher = Slasher::open(config.clone(), logger()).unwrap();
+    let slasher = Slasher::open(config, logger()).unwrap();
 
     let v = vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12];