[docs] [issue23557] Misc/SpecialBuilds.txt contains outdated information about PYMALLOC_DEBUG

Change by Serhiy Storchaka <storchaka+cpython@gmail.com>: ---------- nosy: +vstinner versions: +Python 3.10, Python 3.6, Python 3.7, Python 3.8, Python 3.9 -Python 2.7 _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue23557> _______________________________________