test: remove wallet dependency from feature_nulldummy.py

This test can now be run even with the Bitcoin Core wallet disabled.

test/functional/test_runner.py

@@ -244,8 +244,7 @@ BASE_SCRIPTS = [
     'rpc_generate.py',
     'wallet_balance.py --legacy-wallet',
     'wallet_balance.py --descriptors',
-    'feature_nulldummy.py --legacy-wallet',
-    'feature_nulldummy.py --descriptors',
+    'feature_nulldummy.py',
     'mempool_accept.py',
     'mempool_expiry.py',
     'wallet_import_rescan.py --legacy-wallet',