boards: panasonic: remove arduino_gpio from pan178x_evb boards

Remove arduino_gpio from supported features on pan1781_evb and
pan1782_evb boards due to them expsosing only a "reduced" Arduino header
see compatible panasonic,reduced-arduino-header

Fixes test failures in weekly CI run.

west twister -p pan1782_evb/nrf52833 -s drivers.gpio.st_2pin_arduino

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>