Code cleanup, use pathlib, use pytest keyboard

Clean up checks and logics that are unnecessary due to MILC updates.
Use pathlib instead of os.path for readability.
Use the 'pytest' keyboard for the tests.
Add community layout for 'handwired/onekey/pytest' so we can test
community layouts.

keyboards/handwired/onekey/rules.mk

@@ -20,3 +20,4 @@ FAUXCLICKY_ENABLE = no      # Use buzzer to emulate clicky switches
 HD44780_ENABLE = no         # Enable support for HD44780 based LCDs (+400)
 
 DEFAULT_FOLDER = handwired/onekey/promicro
+LAYOUTS = ortho_1x1