removed non-existent reference

Author: smartvinnetou

pandas/core/series.py

@@ -1424,7 +1424,7 @@ def to_string(
                 with open(buf, "w") as f:
                     f.write(result)
 
-    @doc(NDFrame.to_markdown, klass="Series")
+    @doc(klass=_shared_doc_kwargs["klass"])
     def to_markdown(
         self, buf: Optional[IO[str]] = None, mode: Optional[str] = None, **kwargs
     ) -> Optional[str]: