perf evsel: Rename perf_evsel__is_*() to evsel__is*()

As those are 'struct evsel' methods, not part of tools/lib/perf/, aka
libperf, to whom the perf_ prefix belongs.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-top.c

@@ -298,8 +298,7 @@ static void perf_top__resort_hists(struct perf_top *t)
 		hists__collapse_resort(hists, NULL);
 
 		/* Non-group events are considered as leader */
-		if (symbol_conf.event_group &&
-		    !perf_evsel__is_group_leader(pos)) {
+		if (symbol_conf.event_group && !evsel__is_group_leader(pos)) {
 			struct hists *leader_hists = evsel__hists(pos->leader);
 
 			hists__match(leader_hists, hists);