bpo-36953: Delay removal of ABCs from collections.

Bump the removal to 3.9, indicate collections.abc available since 3.3,
replace version-changed directive tdeprecated-removed.

Author: Carreau

Doc/library/collections.rst

@@ -33,10 +33,10 @@ Python's general purpose built-in containers, :class:`dict`, :class:`list`,
 :class:`UserString`     wrapper around string objects for easier string subclassing
 =====================   ====================================================================
 
-.. versionchanged:: 3.3
+.. deprecated-removed:: 3.3 3.9
     Moved :ref:`collections-abstract-base-classes` to the :mod:`collections.abc` module.
     For backwards compatibility, they continue to be visible in this module through
-    Python 3.7.  Subsequently, they will be removed entirely.
+    Python 3.7.
 
 
 :class:`ChainMap` objects

Lib/collections/__init__.py

@@ -47,8 +47,8 @@ def __getattr__(name):
         obj = getattr(_collections_abc, name)
         import warnings
         warnings.warn("Using or importing the ABCs from 'collections' instead "
-                      "of from 'collections.abc' is deprecated, "
-                      "and in 3.8 it will stop working",
+                      "of from 'collections.abc' is deprecated since Python 3.3,"
+                      "and in 3.9 it will stop working",
                       DeprecationWarning, stacklevel=2)
         globals()[name] = obj
         return obj