perf report: Speed up exit path

When cmd_record exits the whole perf binary will exit right after,
so no need to traverse lots of complex data structures freeing them.

Sticked a comment for leak detectives and for a experiment with obstacks
to be performed so that we can speed up freeing that memory.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>