[Python-mode] Simplifying python-mode.el

[Andreas Röhler]

Hi folks,

consider to simplify python-mode.el core a little bit, removing
presumely unused forms.

For example reduce the number of addressed executables: keeping
python3 and python2, but removing python2.7. Respective at IPythons
side. Several minor changes already done these days.

Please don't hesitate to tell us should something unwanted happen.

Cheers,
Andreas

https://gitlab.com/groups/python-mode-devs