perf ordered_events: Stop using tool->ordered_events

perf ordered_events: Stop using tool->ordered_events

To figure out if ordered_events are being used when doing a flush
operation, it is enough to check if there were in fact some events
queued, i.e. look at oe->nr_events.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-1c5r404vy766kt5nflv88uag@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>