Revert "Network Service: Fix linux-perf-fyi perf histogam metrics' name issue"

This reverts commit feeccd78af9d3bb162771ba973868379f64651b0.

Reason for revert:
linux-perf-fyi bot failed at:
https://ci.chromium.org/p/chrome/builders/luci.chrome.ci/linux-perf-fyi/1823

Original change's description:
> Network Service: Fix linux-perf-fyi perf histogam metrics' name issue
> 
> Currently the histogram metrics' name all start with cold@@ or warm@@,
> This CL removes these prefixes so that the linux-perf-fyi dashboard
> can correctly parse these metrics.
> 
> Bug: 930764
> Change-Id: I12e8c14a841f327c0f094988186b5e8c73a73b12
> Reviewed-on: https://chromium-review.googlesource.com/c/1464640
> Reviewed-by: Simon Hatch <simonhatch@chromium.org>
> Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
> Commit-Queue: Jun Cai <juncai@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#631004}

TBR=simonhatch@chromium.org,crouleau@chromium.org,juncai@chromium.org

Change-Id: I5b2497bf20eddfe2f06830d5db39213c75b9064d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 930764
Reviewed-on: https://chromium-review.googlesource.com/c/1466286
Reviewed-by: Jun Cai <juncai@chromium.org>
Commit-Queue: Jun Cai <juncai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631199}
diff --git a/tools/perf/contrib/network_service/loading.py b/tools/perf/contrib/network_service/loading.py
index aa9186b..ed5f416f 100644
--- a/tools/perf/contrib/network_service/loading.py
+++ b/tools/perf/contrib/network_service/loading.py
@@ -83,7 +83,6 @@
     if chart_name == 'trace':
       continue
     chart = charts[chart_name]
-    chart_name = chart_name.split('@@', 1)[-1]
     new_chart_name = chart_name + suffix
     for point_name in chart:
       chart[point_name]['name'] = new_chart_name