Replaced mbedtls_ssl_safer_memcmp with mbedtls_platform_memcmp

Saves some bytes and mbedtls_platform_memcmp is a bit safer for side channel
attacks.
diff --git a/include/mbedtls/compat-1.3.h b/include/mbedtls/compat-1.3.h
index a58b4724..6e0fb8d 100644
--- a/include/mbedtls/compat-1.3.h
+++ b/include/mbedtls/compat-1.3.h
@@ -2231,7 +2231,7 @@
 #define rsa_rsassa_pss_verify_ext mbedtls_rsa_rsassa_pss_verify_ext
 #define rsa_self_test mbedtls_rsa_self_test
 #define rsa_set_padding mbedtls_rsa_set_padding
-#define safer_memcmp mbedtls_ssl_safer_memcmp
+#define safer_memcmp mbedtls_platform_memcmp
 #define set_alarm mbedtls_set_alarm
 #define sha1 mbedtls_sha1
 #define sha1_context mbedtls_sha1_context
diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index 826581a..4872f6f 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -1159,26 +1159,6 @@
 int mbedtls_ssl_session_copy( mbedtls_ssl_session *dst,
                               const mbedtls_ssl_session *src );
 
-/* constant-time buffer comparison */
-static inline int mbedtls_ssl_safer_memcmp( const void *a, const void *b, size_t n )
-{
-    size_t i;
-    volatile const unsigned char *A = (volatile const unsigned char *) a;
-    volatile const unsigned char *B = (volatile const unsigned char *) b;
-    volatile unsigned char diff = 0;
-
-    for( i = 0; i < n; i++ )
-    {
-        /* Read volatile data in order before computing diff.
-         * This avoids IAR compiler warning:
-         * 'the order of volatile accesses is undefined ..' */
-        unsigned char x = A[i], y = B[i];
-        diff |= x ^ y;
-    }
-
-    return( diff );
-}
-
 #if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1) || \
     defined(MBEDTLS_SSL_PROTO_TLS1_1)
 int mbedtls_ssl_get_key_exchange_md_ssl_tls( mbedtls_ssl_context *ssl,