remove unused tsk_thread from asm-offsets_64.c

I was looking for where tsk_thread is used in the x86_64 code, and couln't find it anywhere. I took it out and compiled the kernel, and it compiled fine.

So this patch simply removes the "thread" from asm-offsets.c since I can't find an owner for it.

index d1b6ed9..40f4175 100644
@@ -38,7 +38,6 @@ int main(void)
 #define ENTRY(entry) DEFINE(tsk_ ## entry, offsetof(struct task_struct, entry))
 	ENTRY(state);
 	ENTRY(flags); 
-	ENTRY(thread); 
 	ENTRY(pid);
 	BLANK();
 #undef ENTRY