perf stat: Revert checks for duration_time

This reverts e864c5ca ("perf stat: Hide internal duration_time
counter") but doing it manually since the code has now moved to a
different file.

The next patch will properly implement duration_time as a full event, so
no need to hide it anymore.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20190326221823.11518-2-andi@firstfloor.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>