OpenGL2: Remove map color scaling and r_forceSunMapLightScale.

Also simplify overbright code in ComputeShaderColors().

code/renderergl2/tr_image.c

@@ -2845,11 +2845,7 @@ void R_SetColorMappings( void ) {
 	int		inf;
 
 	// setup the overbright lighting
-#if defined(USE_OVERBRIGHT)
 	tr.overbrightBits = r_overBrightBits->integer;
-#else
-	tr.overbrightBits = 0;
-#endif
 
 	// allow 2 overbright bits
 	if ( tr.overbrightBits > 2 ) {