If LBR$DELETE_KEY finds the key specified by key_name in the
    current index, it deletes the key. Note that if you want to
    delete a library module, you must first use LBR$DELETE_KEY to
    delete all the keys that point to it, then use LBR$DELETE_DATA to
    delete the module's header and associated data. You cannot call
    LBR$DELETE_KEY from within the user-supplied routine specified in
    LBR$SEARCH or LBR$GET_INDEX.