Why this change?
Since discourse/discourse@a440e15, we have started to support objects typed theme setting so we are switching this theme component to use it instead as it provides a much better UX for configuring the settings required for the theme component.
This partially reverts commit 87404864d20f318629a1413383c76b8ce4bfd398.
Compatibility issue is causing the theme to break: https://meta.discourse.org/t/-/282144