Remove task.scheduler tracing category from slow-reports

This category was not useful. It's adding a trace event for each
top-level post-task, which is about doubling the size of a trace.

Let remove it.

R=oysteine@chromium.org

Change-Id: I271f5314179e7ae6299835c36a0f92a6506eae08
Reviewed-on: https://chromium-review.googlesource.com/c/1301838
Reviewed-by: Eric Seckler <eseckler@chromium.org>
Reviewed-by: oysteine <oysteine@chromium.org>
Commit-Queue: Etienne Bergeron <etienneb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603163}

content/browser/tracing/background_tracing_manager_impl.cc

@@ -676,7 +676,6 @@ TraceConfig BackgroundTracingManagerImpl::GetConfigForCategoryPreset(
       auto config = TraceConfig(
           "benchmark,toplevel,ipc,base,browser,navigation,omnibox,ui,shutdown,"
           "safe_browsing,task_scheduler,"
-          "disabled-by-default-task_scheduler_diagnostics,"
           "disabled-by-default-system_stats,disabled-by-default-cpu_profiler",
           record_mode);
       // Filter only browser process events.
@@ -692,7 +691,6 @@ TraceConfig BackgroundTracingManagerImpl::GetConfigForCategoryPreset(
           "disabled-by-default-v8.gc,"
           "disabled-by-default-blink_gc,"
           "disabled-by-default-renderer.scheduler,"
-          "disabled-by-default-task_scheduler_diagnostics,"
           "disabled-by-default-system_stats,disabled-by-default-cpu_profiler",
           record_mode);
     case BackgroundTracingConfigImpl::CategoryPreset::BLINK_STYLE: