boards: arm: drop counter from board yaml

Remove 'counter' as a supported feature on several NRF boards as these
boards fail to build tests/drivers/counter/counter_basic_api.  This is
due to the fact that we either need explicit board conf files for the
test or have the counter driver enabled via Kconfig.

Fixes #15460

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>