Merge bitcoin/bitcoin#34920: wallet: drop stale TODOs

1438165b1f wallet: drop stale TODOs (Sjors Provoost)

Pull request description:

  I don't remember why I added them. There's also no test that demonstrates the problem, or an open issue requesting a fix.

  It's also unclear if this even _should_ be changed: https://github.com/bitcoin/bitcoin/pull/34912#issuecomment-4121780033

ACKs for top commit:
  polespinasa:
    ACK 1438165b1f
  kevkevinpal:
    ACK [1438165](1438165b1f)
  w0xlt:
    ACK 1438165b1f

Tree-SHA512: 5b6024f38222444488ea3892d1b32277a4091d9c17bc4e8d54efda4d8b8ec567fe639b07fe5bfb26fc9cb8a783bac455dd143f1d731ce111449c9a3aec13368d

src/wallet/external_signer_scriptpubkeyman.cpp

@@ -88,7 +88,6 @@ std::optional<PSBTError> ExternalSignerScriptPubKeyMan::FillPSBT(PartiallySigned
     // Already complete if every input is now signed
     bool complete = true;
     for (const auto& input : psbt.inputs) {
-        // TODO: for multisig wallets, we should only care if all _our_ inputs are signed
         complete &= PSBTInputSigned(input);
     }
     if (complete) return {};
@@ -104,7 +103,7 @@ std::optional<PSBTError> ExternalSignerScriptPubKeyMan::FillPSBT(PartiallySigned
         LogWarning("Failed to sign: %s\n", failure_reason);
         return PSBTError::EXTERNAL_SIGNER_FAILED;
     }
-    if (finalize) FinalizePSBT(psbt); // This won't work in a multisig setup
+    if (finalize) FinalizePSBT(psbt);
     return {};
 }
 } // namespace wallet