How can I delete photo Attachment Pages permanently?

I did a really stupid thing and started clicking the “Link Thumbnails to: Attachment Page” button when adding galleries to about 100 of my posts, and Google went through and indexed every single photo’s attachment page. The photo attachments all have similar names and descriptions to that of my posts, and as a result it’s really screwing with my Google Search placement.

I went through and changed all of the galleries to “Link Thumbnails to: Image File” on every individual post, but I can see that all of the Attachment pages still exist even though there’s no way to get to them now from the posts, and they continue to mess with my Google placement.

Is there any way to permanently delete these picture attachment pages, so that Google will see they no longer exist and unindex them?