perf buildid-list: No need to process the header sections again

As it is already processed by:

	perf_session__new
		perf_session__open
			perf_session__read

This was harmless, because we use dsos__findnew, that would
already find it, but is unnecessary work and removing it makes
builtin-buildid-list.c even shorter.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1262901583-8074-1-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>