platform_util: remove declarations of MBEDTLS_INTERNAL_VALIDATE[_RET]()

These macros end up as being always "empty", so they
can be removed.

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/include/mbedtls/platform_util.h b/include/mbedtls/platform_util.h
index cba02ab..1b371ef 100644
--- a/include/mbedtls/platform_util.h
+++ b/include/mbedtls/platform_util.h
@@ -23,10 +23,6 @@
 extern "C" {
 #endif
 
-/* Internal macros meant to be called only from within the library. */
-#define MBEDTLS_INTERNAL_VALIDATE_RET(cond, ret)  do { } while (0)
-#define MBEDTLS_INTERNAL_VALIDATE(cond)           do { } while (0)
-
 /* Internal helper macros for deprecating API constants. */
 #if !defined(MBEDTLS_DEPRECATED_REMOVED)
 #if defined(MBEDTLS_DEPRECATED_WARNING)