[BUG]: Cleanup docs/howto/howto-install-raspios64.md

[gmacario]

Description of the bug

File howto-install-raspios64.md under docs/howto sometimes mixes up rpi4gm35 (a Raspberry Pi 4B where I originally installed Raspberry Pi OS 32-bit and depthai_demo) with rpi3mv38 (a Raspberry Pi 3B+ where I have been testing Raspberry Pi OS 64-bit, k3s, k9s, etc).

Try repeating the procedure from scratch on a new Raspberry Pi 3B+ (or Raspberry Pi 4 if I can get one), verify that everything works and update the doc accordingly.

Steps To Reproduce

1. Read howto-install-raspios64.md
2. Search for "rpi4gm35" --> There should not be any occurrencies
3. Search for "armv7" --> There should not be any occurrencies

Additional Information

No response

[gmacario]

Fix via #323