Remove Python 2 support
It's dead. Let it rest.
Part of !1604 (merged), offloaded here to speed up review and merging.
Test Plan
N/A, we do not use Python 2 in any of our supported platforms.
Formalities Checklist
-
I confirmed this builds. -
I confirmed Krita ran and the relevant functions work. -
I tested the relevant unit tests and can confirm they are not broken. (If not possible, don't hesitate to ask for help!) -
I made sure my commits build individually and have good descriptions as per KDE guidelines. -
I made sure my code conforms to the standards set in the HACKING file. -
I can confirm the code is licensed and attributed appropriately, and that unattributed code is mine, as per KDE Licensing Policy.