test: ignore --v2transport for older versions instead of asserting

Otherwise, a run with
test_runner.py --v2transport=1 --previous-releases --extended
would hit the removed assert for wallet_backwards_compatibility.py

test/functional/test_framework/test_node.py

@@ -136,9 +136,7 @@ class TestNode():
                 self.args.append("-v2transport=1")
             else:
                 self.args.append("-v2transport=0")
-        else:
-            # v2transport requested but not supported for node
-            assert not v2transport
+        # if v2transport is requested via global flag but not supported for node version, ignore it
 
         self.cli = TestNodeCLI(bitcoin_cli, self.datadir_path)
         self.use_cli = use_cli