pythongh-101815: fix functools.cached_property key sharing doc warnings

Author: carljm

Doc/library/functools.rst

@@ -86,20 +86,17 @@ The :mod:`functools` module defines the following functions:
    The cached value can be cleared by deleting the attribute.  This
    allows the *cached_property* method to run again.
 
-   Note, this decorator interferes with the operation of :pep:`412`
-   key-sharing dictionaries.  This means that instance dictionaries
-   can take more space than usual.
-
-   Also, this decorator requires that the ``__dict__`` attribute on each instance
-   be a mutable mapping. This means it will not work with some types, such as
+   This decorator requires that the ``__dict__`` attribute on each instance be a
+   mutable mapping. This means it will not work with some types, such as
    metaclasses (since the ``__dict__`` attributes on type instances are
    read-only proxies for the class namespace), and those that specify
-   ``__slots__`` without including ``__dict__`` as one of the defined slots
-   (as such classes don't provide a ``__dict__`` attribute at all).
+   ``__slots__`` without including ``__dict__`` as one of the defined slots (as
+   such classes don't provide a ``__dict__`` attribute at all). Also, accessing
+   ``__dict__`` can cause object instances to use slightly more memory.
 
-   If a mutable mapping is not available or if space-efficient key sharing
-   is desired, an effect similar to :func:`cached_property` can be achieved
-   by a stacking :func:`property` on top of :func:`cache`::
+   If a mutable mapping is not available, an effect similar to
+   :func:`cached_property` can be achieved by a stacking :func:`property` on top
+   of :func:`cache`::
 
        class DataSet:
            def __init__(self, sequence_of_numbers):