Simplification and cleanup of windows opengl initialization.

Removed r_colorbits, use desktop color depth as default value. Nevertheless if there are issues when looking
for corresponding pixel format it is still posible to obtain pixel format with color depth that is different
from desktop color.
No changes to game modules, which means that game UI can still set r_colorbits but it has no effect.

src/engine/client/cl_cin.c

@@ -52,7 +52,6 @@ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 
 #define MAX_VIDEO_HANDLES	16
 
-extern glconfig_t glConfig;
 extern	int		s_paintedtime;
 extern	int		s_rawend;