perf tools: Move path related functions to util/path.h

Disentangling util.h header mess a bit more.

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-aj6je8ly377i4upedmjzdsq6@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/util.c

@@ -713,16 +713,6 @@ out:
 	return tip;
 }
 
-bool is_regular_file(const char *file)
-{
-	struct stat st;
-
-	if (stat(file, &st))
-		return false;
-
-	return S_ISREG(st.st_mode);
-}
-
 int fetch_current_timestamp(char *buf, size_t sz)
 {
 	struct timeval tv;