perf_events: Revert: Fix transaction recovery in group_sched_in()

This patch reverts commit 8e5fc1a7 (perf_events: Fix transaction
recovery in group_sched_in()) because it had one flaw in case the
group could never be scheduled. It would cause time_enabled to get
negative.

Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <4cbeeeb7.0aefd80a.6e40.0e2f@mx.google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>