tls13: Adjust include files

- remove duplicate and unused included
- Adjust the order to system, mbedtls global, local.

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index 761c00e..0aecb35 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -28,16 +28,14 @@
 #include "mbedtls/oid.h"
 #include "mbedtls/platform.h"
 #include "mbedtls/constant_time.h"
-#include <string.h>
+#include "psa/crypto.h"
+#include "mbedtls/psa_util.h"
 
 #include "ssl_misc.h"
 #include "ssl_tls13_invasive.h"
 #include "ssl_tls13_keys.h"
 #include "ssl_debug_helpers.h"
 
-#include "psa/crypto.h"
-#include "mbedtls/psa_util.h"
-
 const uint8_t mbedtls_ssl_tls13_hello_retry_request_magic[
                 MBEDTLS_SERVER_HELLO_RANDOM_LEN ] =
                     { 0xCF, 0x21, 0xAD, 0x74, 0xE5, 0x9A, 0x61, 0x11,