tests: all: Remove assignment to promptless NET_GPTP_CLOCK_ACCURACY
tests: all: Remove assignment to promptless NET_GPTP_CLOCK_ACCURACY

Assignments have no effect on promptless symbols. Flagged by
https://github.com/zephyrproject-rtos/zephyr/pull/20742.

Also remove the assignments to the other NET_GPTP_CLOCK_ACCURACY_*
symbols. They are all in the same choice (in
subsys/net/l2/ethernet/gptp/Kconfig), meaning only one of them can be
enabled, and the choice already defaults to
NET_GPTP_CLOCK_ACCURACY_UNKNOWN, which is the symbol assigned last.

The symbol assigned last becomes the choice selection when multiple
symbols in a choice are assigned to. The other choice symbols still
become n. Dependencies override assignments.

Signed-off-by: Ulf Magnusson <01743f1c1deb1fe75271d62edb65757d98ac0bcb@nordicsemi.no>

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