chore: remove SHA2 digest engine implementation

src/digest_engine/sha2_digest.rs

@@ -1,31 +0,0 @@
-use std::io;
-use sha2::{Digest, Sha256};
-
-#[derive(Debug, Clone, Default)]
-pub struct DigestEngineSha256 {
-    hasher: Sha256,
-}
-
-impl DigestEngineSha256 {
-    pub fn new() -> DigestEngineSha256 {
-        DigestEngineSha256 { hasher: Sha256::new() }
-    }
-}
-
-use crate::digest_engine::DigestEngine;
-
-impl DigestEngine for DigestEngineSha256 {
-    fn create(&self) -> Box<dyn DigestEngine> {
-        Box::new(Self::new())
-    }
-
-    fn update(&mut self, data: &[u8]) -> io::Result<()> {
-        self.hasher.update(data);
-        Ok(())
-    }
-
-    fn finalize(&mut self) -> io::Result<String> {
-        let result = self.hasher.clone().finalize();
-        Ok(format!("{:x}", result))
-    }
-}