bpo-33461: emit DeprecationWarning when json.loads(encoding=...) is used (GH-6762)

diff --git a/Doc/library/json.rst b/Doc/library/json.rst
index 589e86c..b476c37 100644
--- a/Doc/library/json.rst
+++ b/Doc/library/json.rst
@@ -265,18 +265,21 @@
       *fp* can now be a :term:`binary file`. The input encoding should be
       UTF-8, UTF-16 or UTF-32.
 
-.. function:: loads(s, *, encoding=None, cls=None, object_hook=None, parse_float=None, parse_int=None, parse_constant=None, object_pairs_hook=None, **kw)
+.. function:: loads(s, *, cls=None, object_hook=None, parse_float=None, parse_int=None, parse_constant=None, object_pairs_hook=None, **kw)
 
    Deserialize *s* (a :class:`str`, :class:`bytes` or :class:`bytearray`
    instance containing a JSON document) to a Python object using this
    :ref:`conversion table <json-to-py-table>`.
 
    The other arguments have the same meaning as in :func:`load`, except
-   *encoding* which is ignored and deprecated.
+   *encoding* which is ignored and deprecated since Python 3.1.
 
    If the data being deserialized is not a valid JSON document, a
    :exc:`JSONDecodeError` will be raised.
 
+   .. deprecated-removed:: 3.1 3.9
+      *encoding* keyword argument.
+
    .. versionchanged:: 3.6
       *s* can now be of type :class:`bytes` or :class:`bytearray`. The
       input encoding should be UTF-8, UTF-16 or UTF-32.