sign: Remove duplicate sigversion check

Also improves documentation in the SignMuSig2 function.

src/script/sign.cpp

@@ -87,8 +87,6 @@ std::optional<uint256> MutableTransactionSignatureCreator::ComputeSchnorrSignatu
 
 bool MutableTransactionSignatureCreator::CreateSchnorrSig(const SigningProvider& provider, std::vector<unsigned char>& sig, const XOnlyPubKey& pubkey, const uint256* leaf_hash, const uint256* merkle_root, SigVersion sigversion) const
 {
-    assert(sigversion == SigVersion::TAPROOT || sigversion == SigVersion::TAPSCRIPT);
-
     CKey key;
     if (!provider.GetKeyByXOnly(pubkey, key)) return false;
 
@@ -342,7 +340,7 @@ static bool SignMuSig2(const BaseSignatureCreator& creator, SignatureData& sigda
                 sigdata.musig2_partial_sigs[pub_key_leaf_hash].emplace(part_pk, partial_sig);
             }
         }
-        // If there are any partial signatures, exit early
+        // If there are any partial signatures, continue with next aggregate pubkey
         auto partial_sigs_it = sigdata.musig2_partial_sigs.find(pub_key_leaf_hash);
         if (partial_sigs_it != sigdata.musig2_partial_sigs.end() && !partial_sigs_it->second.empty()) {
             continue;