Drop unused includes from worker-thread.cc

BUG=none
R=marja@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/302463007

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21530 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/libplatform/worker-thread.cc

@@ -4,8 +4,6 @@
 
 #include "worker-thread.h"
 
-// TODO(jochen): We should have our own version of checks.h.
-#include "../checks.h"
 #include "../../include/v8-platform.h"
 #include "task-queue.h"