message: Remove unused QualityMetricsReporter::Start method from pc test api
  Cr-Commit-Position: refs/heads/master@{#31618}
diff: @@ -420,11 +420,6 @@ class PeerConnectionE2EQualityTestFixture {
  // StopAndReportResults().
  virtual void Start(absl::string_view test_case_name,
  const TrackIdStreamInfoMap* reporter_helper) = 0;
  - // This method has been added for backwards compatibility with upstream
  - // project.
  - void Start(absl::string_view test_case_name) {
  - Start(test_case_name, nullptr);
  - }
  // Invoked by framework after call is ended and peer connection factory and
  // peer connection are destroyed.
  