Stop using MBEDTLS_PRINTF_SIZET

Since Mbed TLS 3.6.0, all officially supported versions of Visual Studio
a printf function family that is sufficiently compliant to C99 for our
purposes, in particular supporting `%zu` for `size_t`. The only platform
without `%zu` that we semi-officially support is older versions of MinGW,
still used in our CI. MinGW provides either a Windows legacy printf or a
standards-compliant printf depending on the value of
`__USE_MINGW_ANSI_STDIO` when compiling each C file. Force the use of the
compliant version. Don't rely on `MBEDTLS_PRINTF_SIZET`, which is defined in
`<mbedtls/debug.h>` and no longer considers the Windows legacy version in
Mbed TLS >= 4.1.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

programs/ssl/ssl_client2.c

@@ -5,14 +5,8 @@
  *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
  */
 
-#define MBEDTLS_ALLOW_PRIVATE_ACCESS
-
-#include "mbedtls/private/pk_private.h"
-
 #include "ssl_test_lib.h"
 
-#include "test/psa_crypto_helpers.h"
-
 #if defined(MBEDTLS_SSL_TEST_IMPOSSIBLE)
 int main(void)
 {
@@ -27,6 +21,8 @@ int main(void)
 }
 #else /* !MBEDTLS_SSL_TEST_IMPOSSIBLE && MBEDTLS_SSL_CLI_C */
 
+#include "test/psa_crypto_helpers.h"
+
 /* Size of memory to be allocated for the heap, when using the library's memory
  * management and MBEDTLS_MEMORY_BUFFER_ALLOC_C is enabled. */
 #define MEMORY_HEAP_SIZE      120000