revert PR 21249

Author: minggli

pandas/core/series.py

@@ -3790,7 +3790,8 @@ def to_csv(self, path=None, index=True, sep=",", na_rep='',
             non-ascii, for python versions prior to 3
         compression : string, optional
             A string representing the compression to use in the output file.
-            Allowed values are 'gzip', 'bz2', 'zip', 'xz'.
+            Allowed values are 'gzip', 'bz2', 'zip', 'xz'. This input is only
+            used when the first argument is a filename.
         date_format: string, default None
             Format string for datetime objects.
         decimal: string, default '.'