perf tools: Remove nr_sort_keys field

The nr_sort_keys field is to carry the number of sort entries in a
hpp_list or hists to determine the depth of indentation of a hist entry.
As it's only used in hierarchy mode and now we have used nr_hpp_node for
this reason, there's no need to keep it anymore.  Let's get rid of it.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1457531222-18130-7-git-send-email-namhyung@kernel.org


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