fix: correct the "plonk" benchmarking (#360)

Author: guorong009

halo2_proofs/benches/plonk.rs

@@ -291,7 +291,7 @@ fn criterion_benchmark(c: &mut Criterion) {
             params,
             pk,
             &[circuit],
-            &[vec![vec![]]],
+            &[vec![]],
             rng,
             &mut transcript,
         )
@@ -302,7 +302,7 @@ fn criterion_benchmark(c: &mut Criterion) {
     fn verifier(params: &ParamsIPA<EqAffine>, vk: &VerifyingKey<EqAffine>, proof: &[u8]) {
         let strategy = SingleStrategy::new(params);
         let mut transcript = Blake2bRead::<_, _, Challenge255<_>>::init(proof);
-        assert!(verify_proof(params, vk, strategy, &[vec![vec![]]], &mut transcript).is_ok());
+        assert!(verify_proof(params, vk, strategy, &[vec![]], &mut transcript).is_ok());
     }
 
     let k_range = 8..=16;