Get rid of deviceinfo_keyboard

Looks like deviceinfo_keyboard is legacy that can be removed. Programs should automatically detect if the device currently has a keyboard or not (oftentimes it can be plugged in anyway). From what I can tell nothing is using this and we can just drop it.

"pmbootstrap init" asks the user about keymaps for the N900, but this feature relies on deviceinfo_keymaps and not on deviceinfo_keyboard.

TODO:

• pmaports MR with commits:
  • device/*: remove deviceinfo_keyboard
  • CI: deviceinfo_keyboard is obsolete
    • add it in deviceinfo_obsolete() in .ci/testcases/test_deviceinfo.py
• pmbootstrap MR: remove deviceinfo_keyboard everywhere -> pmbootstrap!2396 (merged)
• adjust deviceinfo reference wiki page to mark it as deprecated