boards: frdm_k64f: Remove settings pins that don't actually exist
boards: frdm_k64f: Remove settings pins that don't actually exist

On the FRDM-K64F board the SoC uses the 100 pin LQFP package version of
the SoC (MK64FN1M0VLL12).  This pacakge doesn't pin out PTA28 or PTC19.
So remove setting them.

Signed-off-by: Kumar Gala <a5e5248af4cd4f0ed8c515f61d40a6e2db46a66e@linaro.org>

finikorg/zephyr,nashif/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,galak/zephyr,finikorg/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,Vudentz/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,nashif/zephyr,nashif/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,nashif/zephyr,Vudentz/zephyr,finikorg/zephyr