psbt: always put a non_witness_utxo and don't remove it

Offline signers will always need a non_witness_utxo so make sure it is
there.

test/functional/rpc_psbt.py

@@ -38,6 +38,7 @@ class PSBTTest(BitcoinTestFramework):
     def skip_test_if_missing_module(self):
         self.skip_if_no_wallet()
 
+    # TODO: Re-enable this test with segwit v1
     def test_utxo_conversion(self):
         mining_node = self.nodes[2]
         offline_node = self.nodes[0]
@@ -352,7 +353,8 @@ class PSBTTest(BitcoinTestFramework):
         for i, signer in enumerate(signers):
             self.nodes[2].unloadwallet("wallet{}".format(i))
 
-        self.test_utxo_conversion()
+        # TODO: Re-enable this for segwit v1
+        # self.test_utxo_conversion()
 
         # Test that psbts with p2pkh outputs are created properly
         p2pkh = self.nodes[0].getnewaddress(address_type='legacy')