Python tkinter not available on linux

[waffle8946]

tldr use python3Full if on stable and python3Packages.tkinter if on unstable.

Breaking changes announcement for unstable

The full flavor of the Python 3 interpreter is going away. The two features it provided were support for Bluetooth sockets and X11. Bluetooth sockets (socket.AF_BLUETOOTH) will be supported in the default python3 package. The X11 support was used to build tkinter. For nixpkgs this module is not built-in, but instead available from the package set (python3Packages.tkinter). This is a meaningful reduction in the closure size for python3, which is why it was only available in python3Full and i…