This blog post describes how a snippet can be deleted from a single post, page or custom post type.

1. Log-in to your WordPress dashboard.
2. Edit the post, page or custom post type where the snippet has been added.
3. Scroll down to the the “Rich Snippet” metabox.
4. If Rich Snippets have been added to the current post, page or custom post, the plugin will ask if you want to load it. Click “Yes”:

5. After the snippets have been loaded, click the “Delete” button on the right side.
6. Save the page.