Clean up timestamp docs

Author: StanFromIreland

Doc/library/datetime.rst

@@ -1485,13 +1485,6 @@ Instance methods:
    instance. The return value is a :class:`float` similar to that
    returned by :func:`time.time`.
 
-   Naive :class:`.datetime` instances are assumed to represent local
-   time and this method relies on the platform C :c:func:`mktime`
-   function to perform the conversion. Since :class:`.datetime`
-   supports wider range of values than :c:func:`mktime` on many
-   platforms, this method may raise :exc:`OverflowError` or :exc:`OSError`
-   for times far in the past or far in the future.
-
    For aware :class:`.datetime` instances, the return value is computed
    as::
 
@@ -1503,6 +1496,10 @@ Instance methods:
       The :meth:`timestamp` method uses the :attr:`.fold` attribute to
       disambiguate the times during a repeated interval.
 
+   .. versionchanged:: 3.6
+      This method no longer relies on the platform C :c:func:`mktime`
+      function to perform conversions.
+
    .. note::
 
       There is no method to obtain the POSIX timestamp directly from a