Fix duplication of output from test results

https://udn.unrealengine.com/questions/490684/view.html

#jira nojira
#rb none
#lockdown Nick.Penwarden

[CL 5821228 by Andrew Grant in 4.22 branch]

Engine/Source/Developer/AutomationController/Private/AutomationControllerManger.cpp

@@ -1110,6 +1110,8 @@ void FAutomationControllerManager::HandleRunTestsReplyMessage(const FAutomationW
 
 #if WITH_EDITOR
 			FMessageLog AutomationTestingLog("AutomationTestingLog");
+			// we log these messages ourselves for non-editor platforms so suppress this.
+			AutomationTestingLog.SuppressLoggingToOutputLog(true);
 			AutomationTestingLog.Open();
 #endif