Drop unused v8threads include from platform files

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

Review URL: https://codereview.chromium.org/323303002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21788 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/platform-cygwin.cc

@@ -20,7 +20,6 @@
 
 #include "src/base/win32-headers.h"
 #include "src/platform.h"
-#include "src/v8threads.h"
 
 namespace v8 {
 namespace internal {

src/platform-freebsd.cc

@@ -28,7 +28,6 @@
 #undef MAP_TYPE
 
 #include "src/v8.h"
-#include "src/v8threads.h"
 
 #include "src/platform.h"
 

src/platform-linux.cc

@@ -44,7 +44,6 @@
 #include "src/v8.h"
 
 #include "src/platform.h"
-#include "src/v8threads.h"
 
 
 namespace v8 {

src/platform-openbsd.cc

@@ -28,7 +28,6 @@
 #include "src/v8.h"
 
 #include "src/platform.h"
-#include "src/v8threads.h"
 
 
 namespace v8 {

src/platform-qnx.cc

@@ -32,7 +32,6 @@
 #include "src/v8.h"
 
 #include "src/platform.h"
-#include "src/v8threads.h"
 
 
 namespace v8 {

src/platform-solaris.cc

@@ -29,7 +29,6 @@
 #include "src/v8.h"
 
 #include "src/platform.h"
-#include "src/v8threads.h"
 
 
 // It seems there is a bug in some Solaris distributions (experienced in