the extension is stored in the PageNode under the Extensions
property, You should be able to remove it with something like this:
(var api = App.WorkWith())
var pages = api.Pages().LocatedIn(PageLocation.Frontend).ThatArePublished()
You can place this on a regular webforms page codebehind like test.aspx and run it to update the site. As always, be sure to backup the site first just in case.
hope this is helpful!