* Remove some clutter.
* Provide non-suffixed "cmd:"s for default Python version.
* Drop unnecessary gcc BUILD_PREQUIRES, and switch recipe to "any".
* Add missing typing_extensions dependency.
All "cmd:" now work at least with "--version" parameter, except for
`tkconch`, that deadlocks (known issue for Python + Tk: #6967).
- use loops for PROVIDES_pythonxx.
- simplify code where possible.
- remove checks related to x86_gcc2.
It should be easier to add support for newer Python versions now.
