Remove bindable from CircularProgress

[EVAST9919]

There's zero to no reason to have it Bindable imo.
Performance impact is tiny, though in cases such as TestSceneVertexUploadPerformance it's quite noticeable (which is unrealistic, but still).

master	pr

[frenzibyte]

I would look more into whether we can change ValueChangedEvent to a struct rather than slowly turning away from using Bindable in UI components, but turns out it's been attempted before in #6114 and things aren't going good in there.

I think this particular instance makes more sense to not be a bindable though, since it's a continuously changing component, rather than being dependant on user manually changing it (i.e. most other UI components).