Unified multiple definitions of container_of() macro.

Removed duplicate definitions of the container_of() macro and
refactored sources to use the single implementation.

Signed-off-by: Jon A. Cruz <jonc@osg.samsung.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>
diff --git a/src/screenshooter.c b/src/screenshooter.c
index ecf2fdd..b7b8dce 100644
--- a/src/screenshooter.c
+++ b/src/screenshooter.c
@@ -35,6 +35,7 @@
 
 #include "compositor.h"
 #include "screenshooter-server-protocol.h"
+#include "shared/helpers.h"
 
 #include "wcap/wcap-decode.h"