src/meta-raspberrypi:rpi-config: Reduce config.txt size

Remove some comments to reduce config.txt file size to avoid file
corruption and make sure Raspberry Pi 5 will boot successfully.

The issue with large config.txt has been reported to related
projects:
raspberrypi/firmware#1848
Evilpaul/RPi-config#9

This work was sponsored by GOVCERT.LU.

Signed-off-by: Leon Anavi <[email protected]>