tools: Move rbtree.h from tools/perf/

The previous step, copying the contents minus the rcupdate.h parts, was
done as a minimal fix, now do the move from tools/perf/.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-52fllxtsgmtke66pmv98mcma@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>