ext: fiat: Use user-defined assert macro

The libc assert macro was used in curve25519.c even if the user provided
its own definition of the assert macro for MCUboot through
mcuboot_assert.h. This commit fixes this issue.

Signed-off-by: Thomas Altenbach <thomas.altenbach@legrand.com>

ext/fiat/src/curve25519.c

@@ -27,11 +27,10 @@
 //
 // The field functions are shared by Ed25519 and X25519 where possible.
 
-#include <assert.h>
 #include <string.h>
 #include <stdint.h>
 
-#include <mcuboot_config/mcuboot_config.h>
+#include <bootutil/bootutil_public.h>
 
 #if defined(MCUBOOT_USE_MBED_TLS)
 #include <mbedtls/platform_util.h>