misc: assert_post_action: Treat POSIX arch like others
misc: assert_post_action: Treat POSIX arch like others

After #12732, 69045011733b9e97bb8974a22bb83637520f61c1
asserts call k_panic.

Before this, the POSIX arch had its own hack in the
__ASSERT_POST implementation to terminate the process instead
of spining forever.

But the POSIX arch does implement k_panic properly, so there
is no need anymore for this hack.
=> Remove the special treatment for POSIX ARCH

Signed-off-by: Alberto Escolar Piedras <52be3174920ed06cbdfbcf9622a1a6c68e942617@oticon.com>

ldts/zephyr,finikorg/zephyr,explora26/zephyr,ldts/zephyr,nashif/zephyr,galak/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,nashif/zephyr,Vudentz/zephyr,ldts/zephyr,explora26/zephyr,nashif/zephyr,Vudentz/zephyr,explora26/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,explora26/zephyr,explora26/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,Vudentz/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr