[tools] Fix loading old RCS.json files in callstats.html

Change-Id: Ica7e51e8d3e2d41edb0ad98b77e5213fb5f6515a
No-Try: True
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3763864Reviewed-by: Patrick Thier <pthier@chromium.org>
Commit-Queue: Patrick Thier <pthier@chromium.org>
Auto-Submit: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81747}

tools/callstats.html

@@ -1560,7 +1560,7 @@ code is governed by a BSD-style license that can be found in the LICENSE file.
       //  { PAGE: [[metric_name, ...], [...], ]}
       // Also, make sure we don't have the versioned array-style:
       // { VERSION: { PAGE: [[metric_name, ...], [...], ]}, ...}
-      const innerArray = firstProperty(maybeMetrics);
+      const innerArray = firstProperty(maybeMetric);
       if (Array.isArray(maybeMetric) && !Array.isArray(innerArray)) {
         return {
           [getFileName()]: json