soc: snps_arc_hsdk: kconfig: Remove unused CPU_HS38_LINUX symbol
soc: snps_arc_hsdk: kconfig: Remove unused CPU_HS38_LINUX symbol

Added in commit dbc29fe77e ("boards: hsdk: add initial support of ARC HS
Development Kit"), then never used.

Found with a script. CPU_HS38_LINUX was only defined in a
Kconfig.defconfig file.

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

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