Is it possible to delete/remove attachments?

[sverch]

Is it possible to use this library to delete attachments from a PDF file?

I see from #534 that there's a way to get the attachments, but it's not obvious to me from that how to delete them. There's some lifecycle thing going on here with save too, since that function doesn't get the attachments before you call save, which makes me think it's the wrong direction to get the "upstream" state that eventually gets flushed to the actual document.