x86, bts: remove bad warning

In case a ptraced task is reaped (while the tracer is still attached),
ds_exit_thread() is called before ptrace_exit(). The latter will
release the bts_tracer and remove the thread's ds_ctx.
The former will WARN() if the context is not NULL.

Oleg Nesterov submitted patches that move ptrace_exit() before
exit_thread() and thus reverse the order of the above calls.

Remove the bad warning. I will add it again when Oleg's changes are in.
Signed-off-by: NMarkus Metzger <markus.t.metzger@intel.com>
LKML-Reference: <20090305084954.A22000@sedona.ch.intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/ds.c

@@ -1029,5 +1029,4 @@ void ds_copy_thread(struct task_struct *tsk, struct task_struct *father)
 
 void ds_exit_thread(struct task_struct *tsk)
 {
-	WARN_ON(tsk->thread.ds_ctx);
 }