DOC: Remove ..versionchanged less than version 2.0

Author: mroeschke

doc/source/user_guide/io.rst

@@ -303,8 +303,6 @@ compression : {``'infer'``, ``'gzip'``, ``'bz2'``, ``'zip'``, ``'xz'``, ``'zstd'
   As an example, the following could be passed for faster compression and to
   create a reproducible gzip archive:
   ``compression={'method': 'gzip', 'compresslevel': 1, 'mtime': 1}``.
-
-  .. versionchanged:: 1.2.0 Previous versions forwarded dict entries for 'gzip' to ``gzip.open``.
 thousands : str, default ``None``
   Thousands separator.
 decimal : str, default ``'.'``
@@ -1472,7 +1470,7 @@ rather than reading the entire file into memory, such as the following:
    table
 
 
-By specifying a ``chunksize`` to ``read_csv``, the return
+By specifying a ``chunksize`` to :func:`read_csv` as a context manager, the return
 value will be an iterable object of type ``TextFileReader``:
 
 .. ipython:: python
@@ -1482,10 +1480,6 @@ value will be an iterable object of type ``TextFileReader``:
        for chunk in reader:
            print(chunk)
 
-.. versionchanged:: 1.2
-
-  ``read_csv/json/sas`` return a context-manager when iterating through a file.
-
 Specifying ``iterator=True`` will also return the ``TextFileReader`` object:
 
 .. ipython:: python

doc/source/user_guide/visualization.rst

@@ -326,8 +326,6 @@ The ``by`` keyword can be specified to plot grouped histograms:
 
 In addition, the ``by`` keyword can also be specified in :meth:`DataFrame.plot.hist`.
 
-.. versionchanged:: 1.4.0
-
 .. ipython:: python
 
    data = pd.DataFrame(
@@ -480,8 +478,6 @@ columns:
 
 You could also create groupings with :meth:`DataFrame.plot.box`, for instance:
 
-.. versionchanged:: 1.4.0
-
 .. ipython:: python
    :suppress: