Drop lightning-specific code in lightning::crypto

In a few commits, we'll reuse the `chacha20.rs` and `poly1305.rs`
files in a new crate (via symlink). In order to do so, we need to
first avoid any references to things in the `lightning` crate,
which we do here by dropping references to `crate::prelude`.

Author: TheBlueMatt

lightning/src/crypto/chacha20.rs

@@ -342,8 +342,6 @@ pub use self::fuzzy_chacha::ChaCha20;
 mod test {
 	use core::iter::repeat;
 
-	use crate::prelude::*;
-
 	use super::ChaCha20;
 
 	#[test]

lightning/src/crypto/poly1305.rs

@@ -9,8 +9,6 @@
 
 use core::cmp::min;
 
-use crate::prelude::*;
-
 #[derive(Clone, Copy)]
 pub struct Poly1305 {
 	r: [u32; 5],