tests: Cleanup superfluous headers

Mostly remove headers that aren't actually needed for anything.
Add stdint.h to permit dropping xf86drm.h, which is otherwise unneeded.

Signed-off-by: Bryce Harrington <bryce@osg.samsung.com>
Acked-by: Marek Chalupa <mchqwerty@gmail.com>
Tested-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
diff --git a/tests/subsurface-test.c b/tests/subsurface-test.c
index bee249b..cf70017 100644
--- a/tests/subsurface-test.c
+++ b/tests/subsurface-test.c
@@ -22,10 +22,10 @@
 
 #include "config.h"
 
+#include <stdio.h>
 #include <string.h>
 
 #include "weston-test-client-helper.h"
-#include <stdio.h>
 
 #define NUM_SUBSURFACES 3