Revert trailing comma for 3.6<

parso/python/errors.py

@@ -800,18 +800,9 @@ class _ArglistRule(SyntaxRule):
 
             if argument.type == 'argument':
                 first = argument.children[0]
-                if (
-                    argument.children[1].type in _COMP_FOR_TYPES
-                    and len(node.children) >= 2
-                ):
-                    if self._normalizer.version >= (3, 7):
-                        return True
-                    elif len(node.children) == 2 and node.children[1] == ",":
-                        # trailing comma allowed until 3.7
-                        pass
-                    else:
-                        return True
-
+                if argument.children[1].type in _COMP_FOR_TYPES and len(node.children) >= 2:
+                    # a(a, b for b in c)
+                    return True
                 if first in ('*', '**'):
                     if first == '*':
                         if kw_unpacking_only: