When an upstream pipeline set as a trigger for a downstream pipeline is deleted, there is no way to manage the trigger, since the UI spins forever while displaying it.
Instead, here is how the behavior of Pipeline Deletion should be modified:
1. When deleting a pipeline, if the pipeline has outbound triggers, a user should be prompted "The pipeline A is configured to trigger pipelines B, C,... These triggers will be deleted if pipeline A is deleted. Are you sure you want to proceed?", with options "Continue and Cancel"
2. If the user chooses "Continue", the outbound triggers should be deleted.
3. If the user chooses Cancel, the action is aborted.