Revert "[run perf tests] Output to swarming log again."

This reverts commit 7bfe9152.

Reason for revert: crbug.com/1000426 is fixed now, so this is no longer needed.

Original change's description:
> [run perf tests] Output to swarming log again.
> 
> We used to do this before
> https://chromium-review.googlesource.com/c/chromium/src/+/1629432
> We changed it because the swarming was cutting off the logs
> because they were too long (and also loading them was difficult).
> 
> This change is a temporary trial for figuring out crbug.com/1000426
> while we wait for email responses to
> https://groups.google.com/a/google.com/forum/#!topic/luci-eng/3uLbRYVecuc
> 
> 
> Bug: 1000426
> Change-Id: I788d385a665604030f0df93a24e6aab3606929cd
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1790243
> Reviewed-by: John Chen <johnchen@chromium.org>
> Commit-Queue: Caleb Rouleau <crouleau@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#694372}

TBR=crouleau@chromium.org,johnchen@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1000426, 1015505
Change-Id: Ic5b43be621c0719eaec981b54a9a89f22623857f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1864622Reviewed-by: John Chen <johnchen@chromium.org>
Reviewed-by: Juan Antonio Navarro Pérez <perezju@chromium.org>
Auto-Submit: Caleb Rouleau <crouleau@chromium.org>
Commit-Queue: Juan Antonio Navarro Pérez <perezju@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707283}

testing/scripts/run_performance_tests.py

@@ -348,8 +348,9 @@ def execute_telemetry_benchmark(
       return_code = xvfb.run_executable(
           command, env=env, stdoutfile=output_paths.logs)
     else:
-      return_code = test_env.run_command_with_output(
-          command, env=env, stdoutfile=output_paths.logs)
+      with open(output_paths.logs, 'w') as handle:
+        return_code = test_env.run_command_output_to_handle(
+            command, handle, env=env)
     expected_results_filename = os.path.join(temp_dir, 'test-results.json')
     if os.path.exists(expected_results_filename):
       shutil.move(expected_results_filename, output_paths.test_results)