pkcs7: Fix imports

Respond to feedback about duplicate imports[1] and new import style [2].

[1] https://github.com/Mbed-TLS/mbedtls/pull/3431#discussion_r991355485
[2] https://github.com/Mbed-TLS/mbedtls/pull/3431#pullrequestreview-1138745361
Signed-off-by: Nick Child <nick.child@ibm.com>
diff --git a/library/pkcs7.c b/library/pkcs7.c
index ab7bebd..7976a0b 100644
--- a/library/pkcs7.c
+++ b/library/pkcs7.c
@@ -34,17 +34,8 @@
 #include <sys/stat.h>
 #endif
 
-#if defined(MBEDTLS_PLATFORM_C)
 #include "mbedtls/platform.h"
 #include "mbedtls/platform_util.h"
-#else
-#include <stdio.h>
-#include <stdlib.h>
-#define mbedtls_free      free
-#define mbedtls_calloc    calloc
-#define mbedtls_printf    printf
-#define mbedtls_snprintf  snprintf
-#endif
 
 #if defined(MBEDTLS_HAVE_TIME)
 #include "mbedtls/platform_time.h"