mesa/tests: remove unneeded extern C { #include foo } hack

The header itself (enums.h) is already properly annotated.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Reviewed-by: Brian Paul <brianp@vmware.com>

src/mesa/main/tests/enum_strings.cpp

@@ -24,9 +24,7 @@
 #include <gtest/gtest.h>
 #include <GL/gl.h>
 
-extern "C" {
 #include "main/enums.h"
-}
 
 struct enum_info {
    int value;