Use copied instead of map to copy

Clippy emits:

  warning: you are using an explicit closure for copying elements

In one instance we have `map` followed by `flatten`, this can be
replaced by the `flat_map` combinator.

As suggested use `copied` combinator.

src/util/ecdsa.rs

@@ -58,7 +58,7 @@ impl EcdsaSig {
     pub fn to_vec(&self) -> Vec<u8> {
         // TODO: add support to serialize to a writer to SerializedSig
         self.sig.serialize_der()
-            .iter().map(|x| *x)
+            .iter().copied()
             .chain(iter::once(self.hash_ty as u8))
             .collect()
     }

src/util/taproot.rs

@@ -675,7 +675,7 @@ impl TaprootMerkleBranch {
 
     /// Serializes `self` as bytes.
     pub fn serialize(&self) -> Vec<u8> {
-        self.0.iter().map(|e| e.as_inner()).flatten().map(|x| *x).collect::<Vec<u8>>()
+        self.0.iter().flat_map(|e| e.as_inner()).copied().collect::<Vec<u8>>()
     }
 
     /// Appends elements to proof.