python 3.6 removed

[Jon Turney]

Python 3.6 was EOL on December 23, 2021 [1].

Only five years later, I've removed the packages for the python3.6 
interpreter: python36-{,devel,doc,test,tkinter} and idle36.

python3.6 will continue to work where already installed, but it will no 
longer be possible to install it, or any packages which depend upon it.

Work has been done to identify and update the packages which need 
rebuilding for current python3, but not all affected packages have yet 
been updated [2].

If those packages are important to you, please consider helping us to 
bring them up to date [3].

[1] https://devguide.python.org/versions/
[2] https://cygwin.com/packages/reports/python_rebuilds.html
[3] https://cygwin.com/packaging-contributors-guide.html#adopt