Populate "removed_line_items" array when removing items from subscription via admin
Currently the removed line items array in subscription data is not populated when line items are removed via admin.
A customer may remove items from their subscription and then undo that. The removed line items array in the subscription data holds the removed items so they can be added back in case the customer wants to undo it.
I'm proposing that the behavior should be the same in the admin scenario. Alternatively a filter to enable the same behavior.
This would allow an external system to easily keep track of removed items in case the store owner modifies a subscription.