Use to_keypair

Remove the deprecated call to `to_inner` and use the suggested
`to_keypair` function.

Author: tcharding

bitcoind-tests/tests/test_desc.rs

@@ -177,7 +177,7 @@ pub fn test_desc_satisfy(
                 let mut aux_rand = [0u8; 32];
                 rand::thread_rng().fill_bytes(&mut aux_rand);
                 let schnorr_sig =
-                    secp.sign_schnorr_with_aux_rand(&msg, &internal_keypair.to_inner(), &aux_rand);
+                    secp.sign_schnorr_with_aux_rand(&msg, &internal_keypair.to_keypair(), &aux_rand);
                 psbt.inputs[0].tap_key_sig =
                     Some(taproot::Signature { signature: schnorr_sig, sighash_type });
             } else {