perf sched: Cleanup, remove unused variables in map_switch_event()

In map_switch_event(), we don't care the previous process currently,
this patch remove the infomation we get but not used.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
Link: http://lkml.kernel.org/r/1400218625-14613-1-git-send-email-yangds.fnst@cn.fujitsu.com


Signed-off-by: Jiri Olsa <jolsa@kernel.org>