usb: finally remove Kconfig option CONFIG_USB
usb: finally remove Kconfig option CONFIG_USB

After the modules are adapted for the revised
USB device stack configuration, and it seems that
it was only necessary for MCUboot, we can finally
remove Kconfig option CONFIG_USB.

Signed-off-by: Johann Fischer <64a5f06fca6b2d93d742efe564789153170f6198@nordicsemi.no>

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