Remove useless platform macro redefinitions: automatic part

Some source files had code to set mbedtls_xxx aliases when
MBEDTLS_PLATFORM_C is not defined. These aliases are defined unconditionally
by mbedtls/platform.h, so these macro definitions were redundant. Remove
them.

This commit used the following code:
```
perl -i -0777 -pe 's~#if !defined\(MBEDTLS_PLATFORM_C\)\n(#define (mbedtls|MBEDTLS)_.*\n|#include <(stdarg|stddef|stdio|stdlib|string|time)\.h>\n)*#endif.*\n~~mg' $(git grep -l -F '#if !defined(MBEDTLS_PLATFORM_C)')
```

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

programs/test/benchmark.c

@@ -24,13 +24,6 @@
 #endif
 
 #include "mbedtls/platform.h"
-#if !defined(MBEDTLS_PLATFORM_C)
-#include <stdio.h>
-#include <stdlib.h>
-#define mbedtls_exit       exit
-#define mbedtls_printf     printf
-#define mbedtls_free       free
-#endif
 
 #if !defined(MBEDTLS_TIMING_C)
 int main( void )