Simplify _get_argnames()

There's no need to check for emptiness; if they're empty, the list
comprehension already is no-op anyway.

rope/refactor/extract.py

@@ -948,15 +948,13 @@ def _handle_loop_context(self, node):
 
 def _get_argnames(arguments):
     result = []
-    if arguments.posonlyargs:
-        result.extend(node.arg for node in arguments.posonlyargs)
+    result.extend(node.arg for node in arguments.posonlyargs)
     result.extend(node.arg for node in arguments.args if isinstance(node, ast.arg))
     if arguments.vararg:
         result.append(arguments.vararg.arg)
     if arguments.kwarg:
         result.append(arguments.kwarg.arg)
-    if arguments.kwonlyargs:
-        result.extend(node.arg for node in arguments.kwonlyargs)
+    result.extend(node.arg for node in arguments.kwonlyargs)
     return result