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 <marti.bolivar@linaro.org>
diff --git a/boot/zephyr/include/flash_map/flash_map.h b/boot/zephyr/include/flash_map/flash_map.h
index c0c9489..271c50c 100644
--- a/boot/zephyr/include/flash_map/flash_map.h
+++ b/boot/zephyr/include/flash_map/flash_map.h
@@ -51,15 +51,6 @@
     uint32_t fa_size;
 };
 
-extern const struct flash_area *flash_map;
-extern int flash_map_entries;
-
-/*
- * Initializes flash map. Memory will be referenced by flash_map code
- * from this on.
- */
-void flash_map_init(void);
-
 /*
  * Start using flash area.
  */