CFrame: Only re-assign focus when "Render to main" is enabled.

It may cause fullscreen loops and since m_RenderFrame == m_RenderParent now it's not necessary to re-assign focus anymore.

No longer conflicts with PR #683, that PR has been rewritten.
I have no idea, same problem in RendererHasFocus(). I have no idea why native functions are used for everything related to focus.