Fix black screen issues for Active Trader Pro and Assetto Corsa. This reverts commit 4124478b.
For Active Trader Pro, the hack ends up clearing a context that was previously drawn to to black, possibly because multiple OpenGL contexts are involved according to Henri's investigation.
Assetto Corsa creates a D3D device for a window but doesn't actually do any rendering with it. After ceefcca7, having an OpenGL context for a window clears its OpenGL surface to black after its view becomes visible. The OpenGL surface is on top of other layers for the window so the window becomes black after that. The blackness is originally from glDrawBuffer(GL_FRONT_AND_BACK), which presumably prepares a zero-initialized OpenGL front draw buffer. This also suggests that 4124478b is no longer necessary. I could delay the clearToBlackIfNeeded() call so it uses the behavior before ceefcca7, but now that it seems the hack is no longer necessary and might cause more errors. CrossOver has disabled the hack for a while and it seems fine. I think it's time to remove the hack.