If it is Installed from DLS, Obsolete then it is safe to delete. But just because the tag "Obsolete" has been added and it has been replaced by something newer that you have installed does not mean you can safely delete it using Content Manager.
"Built-in, Obsolete" for example, cannot be deleted because it is "Built-in".
"Payware, Obsolete" can only be deleted via the Content Store.