Remove MBEDTLS_SSL_EXPORT_KEYS, making it always on

This option only gated an ability to set a callback,
but was deemed unnecessary as it was yet another define to
remember when writing tests, or test configurations. Fixes #4653.
Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>

programs/ssl/ssl_test_lib.h

@@ -95,8 +95,6 @@
 
 #include "../test/query_config.h"
 
-#if defined(MBEDTLS_SSL_EXPORT_KEYS)
-
 typedef struct eap_tls_keys
 {
     unsigned char master_secret[48];
@@ -122,8 +120,6 @@ typedef struct dtls_srtp_keys
 
 #endif /* MBEDTLS_SSL_DTLS_SRTP */
 
-#endif /* MBEDTLS_SSL_EXPORT_KEYS */
-
 typedef struct
 {
     mbedtls_ssl_context *ssl;