Remove Zeroize Tests (#381)

* Remove Zeroize tests

* Remove `Zeroize` requirements from `Group::Pk`

* Remove `Copy` requirements from `Group::Pk`

* Change to `ZeroizeOnDrop` requirements for `Group::Sk`

* Add note why we don't use `elliptic_curve::PublicKey`

src/key_exchange/tripledh.rs

@@ -109,6 +109,7 @@ where
     Le<<H::Core as BlockSizeUser>::BlockSize, U256>: NonZero,
 {
     server_nonce: GenericArray<u8, NonceLen>,
+    #[derive_where(skip(Zeroize))]
     server_e_pk: PublicKey<G>,
     mac: Output<H>,
 }
@@ -375,6 +376,8 @@ where
     }
 }
 
+/// TODO: implement via derive after hash crates get `Zeroize` support in
+/// `digest` v11.
 impl<G: Group, H: Hash> Drop for Ke2Builder<G, H>
 where
     H::Core: ProxyHash,
@@ -382,21 +385,17 @@ where
     Le<<H::Core as BlockSizeUser>::BlockSize, U256>: NonZero,
 {
     fn drop(&mut self) {
-        struct AssertZeroizeOnDrop<'a, T: ZeroizeOnDrop>(#[allow(unused)] &'a T);
-
         let Self {
             server_nonce,
             transcript_hasher,
-            client_e_pk,
-            server_e_pk,
+            client_e_pk: _,
+            server_e_pk: _,
             shared_secret_1,
             shared_secret_3,
         } = self;
 
         server_nonce.zeroize();
         transcript_hasher.reset();
-        let _ = AssertZeroizeOnDrop(client_e_pk);
-        let _ = AssertZeroizeOnDrop(server_e_pk);
         shared_secret_1.zeroize();
         shared_secret_3.zeroize();
     }
@@ -469,25 +468,3 @@ where
         self.mac.clone()
     }
 }
-
-//////////////////////////
-// Test Implementations //
-//===================== //
-//////////////////////////
-
-#[cfg(test)]
-use crate::serialization::AssertZeroized;
-
-#[cfg(test)]
-impl<H: OutputSizeUser> AssertZeroized for Ke2State<H> {
-    fn assert_zeroized(&self) {
-        let Self {
-            session_key,
-            expected_mac,
-        } = self;
-
-        for byte in session_key.iter().chain(expected_mac) {
-            assert_eq!(byte, &0);
-        }
-    }
-}