OpenGL2: Remove map color scaling and r_forceSunMapLightScale.

Also simplify overbright code in ComputeShaderColors().

code/renderergl2/tr_backend.c

@@ -712,9 +712,6 @@ void	RB_SetGL2D (void) {
 	// set time for 2D shaders
 	backEnd.refdef.time = ri.Milliseconds();
 	backEnd.refdef.floatTime = backEnd.refdef.time * 0.001f;
-
-	// reset color scaling
-	backEnd.refdef.colorScale = 1.0f;
 }