mgmt: updatehub: Clean SHA-256 macros
mgmt: updatehub: Clean SHA-256 macros

Clean SHA-256 macros that were left behind when added flash SHA-256
verification.

Signed-off-by: Gerson Fernando Budke <de7eb9f159f7e30f8dcdecee89db6e1a285bf5b2@ossystems.com.br>

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