perf script: Remove use of die/exit

Allows perf to clean up properly on exit. Only exits left are exec
failures which are appropriate and usage callbacks that list available
options.

Signed-off-by: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1346005487-62961-7-git-send-email-dsahern@gmail.com


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