Remove CTA Modal

[jechols]

The "cta-modal" code is busted when trying to get CSS to pass through to the shadow DOM, and the JS being minified makes it all but impossible to fix ourselves. With the update to Bootstrap 5, this is a major problem in dark mode.

Given that <dialog> now has very wide browser support, it's probably time to just ditch the custom dialog and build something simpler using as much native HTML as is possible, and no component nonsense unless we build that from scratch so we can easily control it.