Transient Subclasses of ABrush default to supporting external packaging

ABrush::SupportsExternalPackaging overrides the base implementation of  AActor::SupportsExternalPackaging which returns false for transient actors, but it doesn't call super. As a result, transient subclasses of ABrush like ADefaultPhysicsVolume return true even if they have the RF_Transient or CLASS_Transient flags. 

• Create an empty project
• Add an empty level (e.g. TestLevel) and save it
• Close Editor
• Run WorldPartitionConvertCommandlet
  • -run=WorldPartitionConvertCommandlet TestLevel.umap -ConversionSuffix -AllowCommandletRendering
  • Will create 3 External Actor files for
    • WorldDataLayers
    • WorldPartitionMiniMap
    • DefaultPhysicsVolume (Transient)
• Run DataValidationCommandlet
  • -Unattended -run=DataValidation
  • Observe error for failure to load an external package, this package was the one created for a transient ADefaultPhysicsVolume
    • LogLevel: Error: Failed to load Actor for External Actor Package /Game/ExternalActors/TestLevel_WP/****