scripted-diff: Use wallets_path and chain_path where possible

Instead of passing the datadir and chain name to os.path.join, just use
the existing properties, which are the same.

-BEGIN VERIFY SCRIPT-
 sed -i --regexp-extended 's|\.datadir, self\.chain, .wallets.|.wallets_path|g' $(git grep -l '\.datadir, self\.chain,')
 sed -i --regexp-extended 's|\.datadir, self\.chain,|.chain_path,|g'            $(git grep -l '\.datadir, self\.chain,')
-END VERIFY SCRIPT-

test/functional/feature_settings.py

@@ -21,7 +21,7 @@ class SettingsTest(BitcoinTestFramework):
 
     def run_test(self):
         node, = self.nodes
-        settings = Path(node.datadir, self.chain, "settings.json")
+        settings = Path(node.chain_path, "settings.json")
         conf = Path(node.datadir, "bitcoin.conf")
 
         # Assert empty settings file was created