test: Set -disablewallet when no wallet has been compiled

self.descriptors is None when no wallet has been compiled, so it is safe
to completely disable the wallet. This change will enhance a future
commit.

test/functional/test_framework/test_node.py

@@ -105,6 +105,9 @@ class TestNode():
             "-debugexclude=rand",
             "-uacomment=testnode%d" % i,
         ]
+        if self.descriptors is None:
+            self.args.append("-disablewallet")
+
         if use_valgrind:
             default_suppressions_file = os.path.join(
                 os.path.dirname(os.path.realpath(__file__)),