perf tools: Get rid of on_exit() feature test

perf tools: Get rid of on_exit() feature test

The on_exit() function was only used in perf record but it's gone in
previous patch.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Stephane Eranian <eranian@google.com>
Cc: Bernhard Rosenkraenzer <Bernhard.Rosenkranzer@linaro.org>
Cc: Irina Tirdea <irina.tirdea@intel.com>
Link: http://lkml.kernel.org/r/1399855645-25815-2-git-send-email-namhyung@kernel.org
Signed-off-by: Jiri Olsa <jolsa@kernel.org>