perf tools: Replace STR() calls with __stringify()

Both do the same thing, the later is the one we get from
linux/stringify.h, i.e. we now use the same function name/practice as
the kernel sources.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-w2sxa5o4bfx7fjrd5mu4zmke@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/util.h

@@ -180,9 +180,6 @@ struct perf_event_attr;
 
 void event_attr_init(struct perf_event_attr *attr);
 
-#define _STR(x) #x
-#define STR(x) _STR(x)
-
 size_t hex_width(u64 v);
 int hex2u64(const char *ptr, u64 *val);