Drop leftover unused kNoThread in platform-openbsd.cc.

src/platform-openbsd.cc

Index: src/platform-openbsd.cc
diff --git a/src/platform-openbsd.cc b/src/platform-openbsd.cc
index 4340094f12986b36cd2b6e8fa69d7b1cb780777c..df08a7a2360eccc5307d4bfd7602fe8aafcfbead 100644
--- a/src/platform-openbsd.cc
+++ b/src/platform-openbsd.cc
@@ -60,10 +60,6 @@
 namespace v8 {
 namespace internal {
 
-// 0 is never a valid thread id on Linux and OpenBSD since tids and pids share a
-// name space and pid 0 is reserved (see man 2 kill).
-static const pthread_t kNoThread = (pthread_t) 0;
-
 
 double ceiling(double x) {
   return ceil(x);