DOC: clean-up 0.23.1 whatsnew (#21368)

(cherry picked from commit 5bbbaf6)

Author: jorisvandenbossche

doc/source/whatsnew/v0.23.1.txt

@@ -13,6 +13,7 @@ and bug fixes. We recommend that all users upgrade to this version.
 .. _whatsnew_0231.fixed_regressions:
 
 Fixed Regressions
+~~~~~~~~~~~~~~~~~
 
 - Reverted the ability of :func:`~DataFrame.to_sql` to perform multivalue
   inserts as this caused regression in certain cases (:issue:`21103`).
@@ -34,87 +35,49 @@ Performance Improvements
 
 - Improved performance of :meth:`CategoricalIndex.is_monotonic_increasing`, :meth:`CategoricalIndex.is_monotonic_decreasing` and :meth:`CategoricalIndex.is_monotonic` (:issue:`21025`)
 - Improved performance of :meth:`CategoricalIndex.is_unique` (:issue:`21107`)
--
--
 
-Documentation Changes
-~~~~~~~~~~~~~~~~~~~~~
-
--
--
 
 .. _whatsnew_0231.bug_fixes:
 
 Bug Fixes
 ~~~~~~~~~
 
 Groupby/Resample/Rolling
-^^^^^^^^^^^^^^^^^^^^^^^^
 
 - Bug in :func:`DataFrame.agg` where applying multiple aggregation functions to a :class:`DataFrame` with duplicated column names would cause a stack overflow (:issue:`21063`)
 - Bug in :func:`pandas.core.groupby.GroupBy.ffill` and :func:`pandas.core.groupby.GroupBy.bfill` where the fill within a grouping would not always be applied as intended due to the implementations' use of a non-stable sort (:issue:`21207`)
 - Bug in :func:`pandas.core.groupby.GroupBy.rank` where results did not scale to 100% when specifying ``method='dense'`` and ``pct=True``
 - Bug in :func:`pandas.DataFrame.rolling` and :func:`pandas.Series.rolling` which incorrectly accepted a 0 window size rather than raising (:issue:`21286`)
 
-Strings
-^^^^^^^
+Data-type specific
 
 - Bug in :meth:`Series.str.replace()` where the method throws `TypeError` on Python 3.5.2 (:issue: `21078`)
-
-Timedelta
-^^^^^^^^^
 - Bug in :class:`Timedelta`: where passing a float with a unit would prematurely round the float precision (:issue: `14156`)
-
-Categorical
-^^^^^^^^^^^
-
-- Bug in :func:`pandas.util.testing.assert_index_equal` which raised ``AssertionError`` incorrectly, when comparing two :class:`CategoricalIndex` objects with param ``check_categorical=False`` (:issue:`19776`)
-- Bug in :meth:`Categorical.fillna` incorrectly raising a ``TypeError`` when `value` the individual categories are iterable and `value` is an iterable (:issue:`21097`, :issue:`19788`)
+- Bug in :func:`pandas.testing.assert_index_equal` which raised ``AssertionError`` incorrectly, when comparing two :class:`CategoricalIndex` objects with param ``check_categorical=False`` (:issue:`19776`)
 
 Sparse
-^^^^^^
 
 - Bug in :attr:`SparseArray.shape` which previously only returned the shape :attr:`SparseArray.sp_values` (:issue:`21126`)
 
-Conversion
-^^^^^^^^^^
-
--
--
-
 Indexing
-^^^^^^^^
 
 - Bug in :meth:`Series.reset_index` where appropriate error was not raised with an invalid level name (:issue:`20925`)
 - Bug in :func:`interval_range` when ``start``/``periods`` or ``end``/``periods`` are specified with float ``start`` or ``end`` (:issue:`21161`)
 - Bug in :meth:`MultiIndex.set_names` where error raised for a ``MultiIndex`` with ``nlevels == 1`` (:issue:`21149`)
-- Bug in :attr:`DatetimeIndex.date` where an incorrect date is returned when the input date has a non-UTC timezone (:issue:`21230`)
 - Bug in :class:`IntervalIndex` constructors where creating an ``IntervalIndex`` from categorical data was not fully supported (:issue:`21243`, issue:`21253`)
 - Bug in :meth:`MultiIndex.sort_index` which was not guaranteed to sort correctly with ``level=1``; this was also causing data misalignment in particular :meth:`DataFrame.stack` operations (:issue:`20994`, :issue:`20945`, :issue:`21052`)
-- Bug in :attr:`DatetimeIndex.time` where given a tz-aware Timestamp, a tz-aware Time is returned instead of tz-naive  (:issue:`21267`)
--
 
 I/O
-^^^
 
 - Bug in IO methods specifying ``compression='zip'`` which produced uncompressed zip archives (:issue:`17778`, :issue:`21144`)
 - Bug in :meth:`DataFrame.to_stata` which prevented exporting DataFrames to buffers and most file-like objects (:issue:`21041`)
--
-
-Plotting
-^^^^^^^^
-
--
--
+- Bug in :meth:`read_stata` and :class:`StataReader` which did not correctly decode utf-8 strings on Python 3 from Stata 14 files (dta version 118) (:issue:`21244`)
 
 Reshaping
-^^^^^^^^^
 
 - Bug in :func:`concat` where error was raised in concatenating :class:`Series` with numpy scalar and tuple names (:issue:`21015`)
 - Bug in :func:`concat` warning message providing the wrong guidance for future behavior (:issue:`21101`)
 
 Other
-^^^^^
 
 - Tab completion on :class:`Index` in IPython no longer outputs deprecation warnings (:issue:`21125`)
-- Bug preventing pandas from being importable with -OO optimization (:issue:`21071`)