Remove unnecessary (and harmful) include

Besides being unnecessary, it was causing problem when build SSL test
programs, which include this header, then in turn trying to include the
internal header from library, which didn't work.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/tests/include/test/psa_crypto_helpers.h b/tests/include/test/psa_crypto_helpers.h
index 753cb43..34a42c4 100644
--- a/tests/include/test/psa_crypto_helpers.h
+++ b/tests/include/test/psa_crypto_helpers.h
@@ -28,10 +28,6 @@
 #include <psa/crypto.h>
 #endif
 
-#if defined(MBEDTLS_USE_PSA_CRYPTO)
-#include "psa_util_internal.h"
-#endif
-
 #if defined(MBEDTLS_MD_LIGHT)
 #include "mbedtls/md.h"
 #endif