- Duke: for camera textures, set display_mirror to 2, not 1.

This avoids actually mirroring the sprites while otherwise retaining the effects on player visibility. Although a value of 1 was working previously it was merely by happenstance, not by design.
Also remove two redundant local copies of display_mirror in Blood and SW.

source/games/blood/src/animatesprite.cpp

@@ -961,8 +961,6 @@ void GameInterface::processSprites(tspriteArray& tsprites, const DVector3& view,
 	viewProcessSprites(tsprites, view, viewang, interpfrac);
 }
 
-int display_mirror;
-
 void GameInterface::EnterPortal(DCoreActor* viewer, int type)
 {
 	if (type == PORTAL_WALL_MIRROR)

source/games/duke/src/render.cpp

@@ -85,7 +85,7 @@ void GameInterface::UpdateCameras(double smoothratio)
 		screen->RenderTextureView(canvas, [=](IntRect& rect)
 			{
 				auto camera = camsprite->GetOwner();
-				display_mirror = 1; // should really be 'display external view'.
+				display_mirror = 2; // should really be 'display external view'.
 				auto cstat = camera->spr.cstat;
 				camera->spr.cstat = CSTAT_SPRITE_INVISIBLE;
 				render_camtex(camera, camera->spr.pos, camera->sector(), DRotator(maphoriz(-camera->spr.shade), camera->interpolatedyaw(smoothratio), nullAngle), tex, rect, smoothratio);

source/games/sw/src/draw.cpp

@@ -64,7 +64,6 @@ extern DCoreActor* wall_to_sprite_actors[8];
 
 BEGIN_SW_NS
 
-int display_mirror;
 static int OverlapDraw = false;
 extern bool QuitFlag, SpriteInfo;
 extern bool Voxel;