Remove some unused imports

examples/set1_6/main.rs

@@ -1,4 +1,4 @@
-use cryptopals::{prelude::*, bvec, bvec64, english::{Bhattacharyya, self}};
+use cryptopals::{prelude::*, bvec64, english::{Bhattacharyya, self}};
 
 fn main() {
     let s1 = b"this is a test".to_vec();

examples/set1_7/main.rs

@@ -1,5 +1,5 @@
 #![feature(array_chunks)]
-use cryptopals::{prelude::*, bvec, bvec64, friendly::aes128};
+use cryptopals::{prelude::*, bvec64, friendly::aes128};
 
 fn main() {
     let key = *b"YELLOW SUBMARINE";