gh-155354: Document that sys._clear_type_cache no longer clears the type cache (#155391)

Author: fedonman

Doc/library/sys.rst

@@ -233,15 +233,15 @@ always available. Unless explicitly noted otherwise, all variables are read-only
 
 .. function:: _clear_type_cache()
 
-   Clear the internal type cache. The type cache is used to speed up attribute
-   and method lookups. Use the function *only* to drop unnecessary references
-   during reference leak debugging.
-
-   This function should be used for internal and specialized purposes only.
+   This function is a no-op. It used to clear the internal type cache, which
+   is now implemented per-type.
 
    .. deprecated:: 3.13
       Use the more general :func:`_clear_internal_caches` function instead.
 
+   .. versionchanged:: 3.16
+      This function is now a no-op.
+
 
 .. function:: _clear_internal_caches()
 
@@ -250,6 +250,9 @@ always available. Unless explicitly noted otherwise, all variables are read-only
 
    .. versionadded:: 3.13
 
+   .. versionchanged:: 3.16
+      The type cache is no longer cleared, as it is now implemented per-type.
+
 
 .. function:: _current_frames()