[benchmarking] stop running ref build for android-pixel2

This CL disabled the reference builds on perf tests of android-pixel2. This tester is picked because among all testers, it has the lowest of anomalies filterd by using reference build.

We will monitor the perf data and how dashboard reacts without the ref data.

Bug: chromium:1108663
Change-Id: I1f2b94383870d9a02579afcb16b02f5f8e6f27ab
Ignore-Cq-Freeze: only affects the config for perf bot to select benchmarks.
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2318985Reviewed-by: Stephen Martinis <martiniss@chromium.org>
Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Wenbin Zhang <wenbinzhang@google.com>
Cr-Commit-Position: refs/heads/master@{#793253}

testing/buildbot/chromium.perf.json

@@ -486,8 +486,7 @@
           "-v",
           "--browser=android-chrome",
           "--upload-results",
-          "--test-shard-map-filename=android-pixel2-perf_map.json",
-          "--run-ref-build"
+          "--test-shard-map-filename=android-pixel2-perf_map.json"
         ],
         "isolate_name": "performance_test_suite",
         "merge": {

tools/perf/core/bot_platforms.py

@@ -466,10 +466,13 @@ ANDROID_NEXUS_5X_WEBVIEW = PerfPlatform(
     'Android Nexus5X WebView Perf', 'Android AOSP MOB30K',
     _ANDROID_NEXUS_5X_WEBVIEW_BENCHMARK_CONFIGS, 16, 'android',
     run_reference_build=False)
-ANDROID_PIXEL2 = PerfPlatform(
-    'android-pixel2-perf', 'Android OPM1.171019.021',
-    _ANDROID_PIXEL2_BENCHMARK_CONFIGS, 35, 'android',
-    executables=_ANDROID_PIXEL2_EXECUTABLE_CONFIGS)
+ANDROID_PIXEL2 = PerfPlatform('android-pixel2-perf',
+                              'Android OPM1.171019.021',
+                              _ANDROID_PIXEL2_BENCHMARK_CONFIGS,
+                              35,
+                              'android',
+                              executables=_ANDROID_PIXEL2_EXECUTABLE_CONFIGS,
+                              run_reference_build=False)
 ANDROID_PIXEL2_WEBVIEW = PerfPlatform(
     'android-pixel2_webview-perf', 'Android OPM1.171019.021',
     _ANDROID_PIXEL2_WEBVIEW_BENCHMARK_CONFIGS, 21, 'android',