Fix for ships blowing up with live debris submodels

[Baezon]

Instead of searching for live debris, and then searching for that debris' parent, and then blowing them up, simply search for the submodels with live debris and blow them up directly. This simplifies the code and entirely skips needing and allows for the deletion of model_get_parent_submodel_for_live_debris which is good because it only handled submodels with live debris if they were a direct child of detail0, and would error if a ship with such a submodel were destroyed.