flash_map: delete obsolete flash_map* declarations
flash_map: delete obsolete flash_map* declarations

The following declarations are undefined and unused in both simulator
and zephyr builds (96b_nitrogen, 96b_carbon, frdm_k64f):

- flash_map
- flash-map_entries
- flash_map_init()

Delete them.

Signed-off-by: Marti Bolivar <9d90ac4c7bf6a305f6bfd81a23c7859bc883380e@linaro.org>

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