zephyr: remove ZEPHYR_BASE "bounce option" from Kconfig
zephyr: remove ZEPHYR_BASE "bounce option" from Kconfig

These are not necessary anymore; kconfiglib evaluates $FOO in the
environment.

Signed-off-by: Marti Bolivar <9d90ac4c7bf6a305f6bfd81a23c7859bc883380e@nordicsemi.no>

runtimeco/mcuboot,runtimeco/mcuboot,tamban01/mcuboot,ATmobica/mcuboot,tamban01/mcuboot,runtimeco/mcuboot,ATmobica/mcuboot,tamban01/mcuboot,runtimeco/mcuboot,utzig/mcuboot,utzig/mcuboot,runtimeco/mcuboot,ATmobica/mcuboot,utzig/mcuboot,tamban01/mcuboot,utzig/mcuboot,ATmobica/mcuboot,ATmobica/mcuboot,tamban01/mcuboot,utzig/mcuboot