Several Windows related cleanups:

Several Windows related cleanups:
* Removed a #define from pyconfig.h. The macro was already defined a few lines higher.
* Fixed path to tix in the build_tkinter.py script
* Changed make_buildinfo.c to use versions of unlink and strcat which are considered safe by Windows (as suggested by MvL).
* Removed two defines from pyproject.vsprops that are no longer required. Both are defined in pyconfig.h and make_buildinfo.c doesn't use the unsafe versions any more (as suggested by MvL).
* Added some more information about PGO and the property files to PCbuild9/readme.txt.

Are you fine with the changes, Martin?