perf evsel: Rename *perf_evsel__*name() to *evsel__*name()

As they are 'struct evsel' methods or related routines, 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-diff.c

@@ -981,7 +981,7 @@ static void data_process(void)
 
 		if (!quiet) {
 			fprintf(stdout, "%s# Event '%s'\n#\n", first ? "" : "\n",
-				perf_evsel__name(evsel_base));
+				evsel__name(evsel_base));
 		}
 
 		first = false;