perf/events/core: Drop unused variable after cleanup

... in 3a497f48 ("perf: Simplify perf_event_exit_task_context()")

Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1399720259-28275-1-git-send-email-bp@alien8.de


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>