board/BuR/common: remove unused function 'blink'

since we have possibility to write out on lcd whats going on, we don't need
the gpio blink functionality anymore.

Signed-off-by: Hannes Petermaier <hannes.petermaier@br-automation.com>

Signed-off-by: Hannes Petermaier <oe5hpm@oevsv.at>