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/wallet_signer.py

@@ -18,6 +18,9 @@ from test_framework.util import (
 
 
 class WalletSignerTest(BitcoinTestFramework):
+    def add_options(self, parser):
+        self.add_wallet_options(parser, legacy=False)
+
     def mock_signer_path(self):
         path = os.path.join(os.path.dirname(os.path.realpath(__file__)), 'mocks', 'signer.py')
         if platform.system() == "Windows":