Refactor ecdsa_sighash_script_code

This method contains duplicate code, for which we already have a method.
As such, the code can be simplified.

This patch does beg the question 'why are we using hardcoded
Network::Bitcoin'?

Author: tcharding

src/descriptor/segwitv0.rs

@@ -380,15 +380,13 @@ impl<Pk: MiniscriptKey + ToPublicKey> Wpkh<Pk> {
         self.spk()
     }
 
-    /// Obtain the pre bip-340 signature script code for this descriptor
-    /// Non failing verion of [`DescriptorTrait::script_code`] for this descriptor
+    /// Obtains the pre bip-340 signature script code for this descriptor.
     pub fn ecdsa_sighash_script_code(&self) -> Script {
         // For SegWit outputs, it is defined by bip-0143 (quoted below) and is different from
         // the previous txo's scriptPubKey.
         // The item 5:
         //     - For P2WPKH witness program, the scriptCode is `0x1976a914{20-byte-pubkey-hash}88ac`.
-        let addr = Address::p2pkh(&self.pk.to_public_key(), Network::Bitcoin);
-        addr.script_pubkey()
+        self.addr(Network::Bitcoin).script_pubkey()
     }
 }