SFixupRedirectorsReport was added with 31698013. There is no way to prevent the UI from showing so the code cannot be used in unattended mode.
Execute the following code from a project that contains file redirectors:
FAssetToolsModule& AssetToolsModule = FModuleManager::LoadModuleChecked<FAssetToolsModule>(TEXT("AssetTools"));
AssetToolsModule.Get().FixupReferencers(Redirectors, false, ERedirectFixupMode::DeleteFixedUpRedirectors);
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-389775 in the post.