Remove `Discourse.SiteSettings` from tests (PR #10193)

These commits add support for this.siteSettings to QUnit tests that need to change settings.

We are still using Discourse.SiteSettings behind the scenes but that should be easier to remove in the future if we stick to this API.


LGTM :+1:

I imagine false is the default and this is why you removed it ?

although we kept it here?

and here

Oh while refactoring I noticed it was not necessary here. I didn’t notice the other places.