[tools/perf] Fix proxy power metric

Sched slices with utid = 0 correspond to the time when CPU is idle,
so they don't contribute to the total power consumption.

Bug: b/155073796
Change-Id: I072b2e9bb8984161518634633d9b4a7bf411eceb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2247893Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Commit-Queue: Mikhail Khokhlov <khokhlov@google.com>
Cr-Commit-Position: refs/heads/master@{#779328}

tools/perf/core/tbmv3/metrics/power_cpu_estimate.sql

@@ -18,7 +18,8 @@ SELECT
 FROM power_per_thread
 WHERE
     ts > (SELECT begin FROM RunStory)
-    AND ts + dur < (SELECT end FROM RunStory);
+    AND ts + dur < (SELECT end FROM RunStory)
+    AND utid != 0;
 
 CREATE VIEW power_cpu_estimate_output AS
 SELECT PowerCpuEstimate(