Remove excessive documentation. Re-target to 3.15.

Author: serhiy-storchaka

Doc/library/mmap.rst

@@ -312,11 +312,10 @@ To map anonymous memory, -1 should be passed as the fileno along with the length
 
       Return the length of the file, which can be larger than the size of the
       memory-mapped area.
+      For anonymous mapping, return its size.
 
-      .. versionchanged:: 3.11
-         For a mapping of anonymous memory, the size is now returned on both
-         Unix and Windows. Previously, the size would be returned on Windows
-         and an :exc:`OSError` would be raised on Unix.
+      .. versionchanged:: next
+         Supports anonymous mapping on Unix.
 
 
    .. method:: tell()

Doc/whatsnew/3.12.rst

@@ -753,15 +753,6 @@ math
   for moving up or down multiple steps at a time. (Contributed by
   Matthias Goergens, Mark Dickinson, and Raymond Hettinger in :gh:`94906`.)
 
-mmap
-----
-
-* The :meth:`~mmap.mmap.size` method of the :class:`mmap.mmap` class
-  now returns the size of an anonymous mapping on both Unix and Windows.
-  Previously, the size would be returned on Windows and an :exc:`OSError` would
-  be raised on Unix.
-  (Contributed by Zackery Spytz in :issue:`43429`.)
-
 os
 --