test: Remove wallet option from non-wallet tests

Review note: The changes are complete, because self.options.descriptors
is set to None in parse_args (test_framework.py).

A value of None implies -disablewallet, see the previous commit.

So if a call to add_wallet_options is missing, it will lead to a test
failure when the wallet is compiled in.

test/functional/example_test.py

@@ -79,6 +79,9 @@ class ExampleTest(BitcoinTestFramework):
     # Override the set_test_params(), skip_test_if_missing_module(), add_options(), setup_chain(), setup_network()
     # and setup_nodes() methods to customize the test setup as required.
 
+    def add_options(self, parser):
+        self.add_wallet_options(parser)
+
     def set_test_params(self):
         """Override test parameters for your individual test.