gh-141004: Mark up docs of old PyMem macros (GH-143783)

These had a docs-only deprecation notice since the first version of the docs in this repo. Nowadays we call things “soft deprecated” if there's just a note in the docs.

The deprecated directive needs a version, I went with the first one that had the notice (2.0; it's not in 1.6):
- https://docs.python.org/release/2.0/api/memoryInterface.html
- https://docs.python.org/release/1.6/api/memoryInterface.html

Since PEP 445, they are now direct aliases; there are no (additional) binary compatibility concerns over the preferred names.