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.
Yeah, likewise, I have no idea. We should work towards converting over calls like these to wx at some point so it makes the UI fully independent from the OS. It'll get rid of headache in terms of form managing (if a bug hits one OS, it'll hit all of them and not just two, making it easier to regression test) and make it easier to transition to Qt.