Use full tuple instead of KeySource

The `KeySource` type is a type alias from `bitcoin::bip32` for a
tuple (fingerprint, derivation_path). In other places in the code we use
the full tuple, we should be uniform and use one or the other. Elect to
use the tuple.

Use full tuple `(FingerPrint, DerivationPath)` instead of `KeySource`.

Author: tcharding

src/descriptor/key.rs

@@ -43,7 +43,7 @@ pub struct DescriptorSinglePub {
 #[derive(Debug)]
 pub struct DescriptorSinglePriv {
     /// Origin information (fingerprint and derivation path).
-    pub origin: Option<bip32::KeySource>,
+    pub origin: Option<(bip32::Fingerprint, bip32::DerivationPath)>,
     /// The private key.
     pub key: bitcoin::PrivateKey,
 }