Fix doc of StooqDailyReader freq argument

_DailyBaseReader does not have the `freq` parameter.

Author: hnishi

pandas_datareader/stooq.py

@@ -27,7 +27,6 @@ class StooqDailyReader(_DailyBaseReader):
         Number of symbols to download consecutively before initiating pause.
     session : Session, default None
         requests.sessions.Session instance to be used
-    freq: string, d, w, m ,q, y for daily, weekly, monthly, quarterly, yearly
 
     Notes
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