// Report was obtained before...
// Report report = ...

report.Open(false, false);

// Remove a wire harness from report sources of this report.
report.RemoveReportSources(report.GetAllWireHarnessInfos().Where(s => s.Name == "harness_00001"));

// Remove a cable unit from report sources of this report.
report.RemoveReportSources(report.GetAllCableUnitInfos().Where(s => s.Name == "Cable unit:1"));

// Remove both - wire harness and cable unit.
List<DerivationSource> desiredSources = new List<DerivationSource>();
desiredSources.AddRange(report.GetAllWireHarnessInfos().Where(s => s.Name == "harness_00001"));
desiredSources.AddRange(report.GetAllCableUnitInfos().Where(s => s.Name == "Cable unit:1"));

report.RemoveReportSources(desiredSources);

// Save and close this report.
report.Save();
report.Close();