Drop cygpty patch for 3.14

It's only needed on Windows 8.1 (0.12% of users) or if you run with "MSYS=disable_pcon".

Removing it would make isatty() return false by default when running in mintty etc. which is mainly visible by Python not starting interactive. Could be worked around by passing `-i` or setting `PYTHONINSPECT=1` if users need to.