Simplify conditional guards in error.c

Simplify the guards on MBEDTLS_ERROR_C and MBEDTLS_ERROR_STRERROR_DUMMY.

No longer include superfluous headers and definition: platform.h is
only needed for MBEDTLS_ERROR_C; time_t is not needed at all.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/scripts/data_files/error.fmt b/scripts/data_files/error.fmt
index 1c8a790..9e479bb 100644
--- a/scripts/data_files/error.fmt
+++ b/scripts/data_files/error.fmt
@@ -19,20 +19,20 @@
 
 #include "common.h"
 
+#include "mbedtls/error.h"
+
+#if defined(MBEDTLS_ERROR_C) || defined(MBEDTLS_ERROR_STRERROR_DUMMY)
+
 #if defined(MBEDTLS_ERROR_C)
-#include <string.h>
-#endif
 
 #if defined(MBEDTLS_PLATFORM_C)
 #include "mbedtls/platform.h"
 #else
 #define mbedtls_snprintf snprintf
-#define mbedtls_time_t   time_t
 #endif
 
-#if defined(MBEDTLS_ERROR_C)
-
 #include <stdio.h>
+#include <string.h>
 
 HEADER_INCLUDED
 
@@ -149,8 +149,6 @@
 
 #else /* MBEDTLS_ERROR_C */
 
-#if defined(MBEDTLS_ERROR_STRERROR_DUMMY)
-
 /*
  * Provide an non-function in case MBEDTLS_ERROR_C is not defined
  */
@@ -162,6 +160,6 @@
         buf[0] = '\0';
 }
 
-#endif /* MBEDTLS_ERROR_STRERROR_DUMMY */
-
 #endif /* MBEDTLS_ERROR_C */
+
+#endif /* MBEDTLS_ERROR_C || MBEDTLS_ERROR_STRERROR_DUMMY */