rpc: deprecate addresses and reqSigs from rpc outputs

1) add a new sane "address" field (for outputs that have an
   identifiable address, which doesn't include bare multisig)
2) with -deprecatedrpc: leave "reqSigs" and "addresses" intact
   (with all weird/wrong behavior they have now)
3) without -deprecatedrpc: drop "reqSigs" and "addresses" entirely,
   always.

test/functional/wallet_send.py

@@ -389,10 +389,10 @@ class WalletSendTest(BitcoinTestFramework):
         assert res["complete"]
         res = self.test_send(from_wallet=w0, to_wallet=w1, amount=1, add_to_wallet=False, change_address=change_address, change_position=0)
         assert res["complete"]
-        assert_equal(self.nodes[0].decodepsbt(res["psbt"])["tx"]["vout"][0]["scriptPubKey"]["addresses"], [change_address])
+        assert_equal(self.nodes[0].decodepsbt(res["psbt"])["tx"]["vout"][0]["scriptPubKey"]["address"], change_address)
         res = self.test_send(from_wallet=w0, to_wallet=w1, amount=1, add_to_wallet=False, change_type="legacy", change_position=0)
         assert res["complete"]
-        change_address = self.nodes[0].decodepsbt(res["psbt"])["tx"]["vout"][0]["scriptPubKey"]["addresses"][0]
+        change_address = self.nodes[0].decodepsbt(res["psbt"])["tx"]["vout"][0]["scriptPubKey"]["address"]
         assert change_address[0] == "m" or change_address[0] == "n"
 
         self.log.info("Set lock time...")