BUILD/MINOR: stats: remove unexpected argument to stats_dump_json_header()

Commit 05ee213 ("MEDIUM: stats: Add JSON output option to show (info|stat)")
used to pass argument "uri" to the aforementionned function which doesn't
take any. It's probably a leftover from multiple iterations of the same
patchset. Spotted by Dmitry Sivachenko. No backport is needed.
diff --git a/src/stats.c b/src/stats.c
index 736852b..8f73b7d 100644
--- a/src/stats.c
+++ b/src/stats.c
@@ -2530,7 +2530,7 @@
 		if (appctx->ctx.stats.flags & STAT_FMT_HTML)
 			stats_dump_html_head(uri);
 		else if (appctx->ctx.stats.flags & STAT_FMT_JSON)
-			stats_dump_json_header(uri);
+			stats_dump_json_header();
 		else if (!(appctx->ctx.stats.flags & STAT_FMT_TYPED))
 			stats_dump_csv_header();