Remove unnecessary include

This is a PSA-based program and psa/crypto.h
is already included.
Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>
diff --git a/programs/psa/key_ladder_demo.c b/programs/psa/key_ladder_demo.c
index 6059fb1..a79fac6 100644
--- a/programs/psa/key_ladder_demo.c
+++ b/programs/psa/key_ladder_demo.c
@@ -58,8 +58,6 @@
 
 #include "mbedtls/platform.h" // for mbedtls_setbuf
 #include "mbedtls/platform_util.h" // for mbedtls_platform_zeroize
-// md.h is included this early since MD_CAN_XXX macros are defined there.
-#include "mbedtls/md.h"
 
 #include <psa/crypto.h>