Clean up the board specific samples:
- Do not hard-code the i2c0 device label in the line follower sample.
- Miscellaneous docs cleanups.
Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>
found some references to files (via :zephyr_file: and :zephyr-app:) that
were moved, so the links were broken
Fixes: #19660
Signed-off-by: David B. Kinder <david.b.kinder@intel.com>