fixup duplicate line

Author: jbrockmendel

doc/source/whatsnew/v0.23.0.txt

@@ -589,7 +589,6 @@ Other API Changes
 - :func:`Series.to_csv` now accepts a ``compression`` argument that works in the same way as the ``compression`` argument in :func:`DataFrame.to_csv` (:issue:`18958`)
 - Set operations (union, difference...) on :class:`IntervalIndex` with incompatible index types will now raise a ``TypeError`` rather than a ``ValueError`` (:issue:`19329`)
 - :class:`DateOffset` objects render more simply, e.g. ``<DateOffset: days=1>`` instead of ``<DateOffset: kwds={'days': 1}>`` (:issue:`19403`)
-- :func:`pandas.merge` provides a more informative error message when trying to merge on timezone-aware and timezone-naive columns (:issue:`15800`)
 - Boolean operations ``&, |, ^`` between a ``Series`` and an ``Index`` will no longer raise ``TypeError`` (:issue:`19792`)
 
 .. _whatsnew_0230.deprecations: