perf data: Rename directory "header" file to "data"

In preparation to support a single file directory format, rename "header"
to "data" because "header" is a mis-leading name when there is only 1 file.
Note, in the multi-file case, the "header" file also contains data.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lore.kernel.org/lkml/20191004083121.12182-4-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/util.c

@@ -185,7 +185,7 @@ static int rm_rf_depth_pat(const char *path, int depth, const char **pat)
 int rm_rf_perf_data(const char *path)
 {
 	const char *pat[] = {
-		"header",
+		"data",
 		"data.*",
 		NULL,
 	};