Remove unneeded namesapcing in header files

Remove the `mbedtls` namesapcing in the `#include` in header files
Resolves issue #857
diff --git a/include/mbedtls/platform.h b/include/mbedtls/platform.h
index 9d9c529..624cc64 100644
--- a/include/mbedtls/platform.h
+++ b/include/mbedtls/platform.h
@@ -40,7 +40,7 @@
 #endif
 
 #if defined(MBEDTLS_HAVE_TIME)
-#include "mbedtls/platform_time.h"
+#include "platform_time.h"
 #endif
 
 #ifdef __cplusplus