Also removes the unused `cgsize_win_from_mac()`.
-- v2: winemac.drv: Remove dead cgsize_win_from_mac() function. winemac.drv: Parametrize retina in cgpoint_win_from_mac(). winemac.drv: Parametrize retina in cgpoint_mac_from_win(). winemac.drv: Parametrize retina in cgsize_mac_from_win(). winemac.drv: Parametrize retina in cgrect_win_from_mac(). winemac.drv: Parametrize retina in cgrect_mac_from_win().