Remove redundant CollisionInfo::plane

src/client/localplayer.cpp

@@ -1196,7 +1196,7 @@ void LocalPlayer::handleAutojump(f32 dtime, Environment *env,
 
 	bool horizontal_collision = false;
 	for (const auto &colinfo : result.collisions) {
-		if (colinfo.type == COLLISION_NODE && colinfo.plane != 1) {
+		if (colinfo.type == COLLISION_NODE && colinfo.axis != COLLISION_AXIS_Y) {
 			horizontal_collision = true;
 			break; // one is enough
 		}

src/collision.cpp

@@ -509,7 +509,6 @@ collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 			info.object = nearest_info.obj;
 			info.new_pos = *pos_f;
 			info.old_speed = *speed_f;
-			info.plane = nearest_collided;
 
 			// Set the speed component that caused the collision to zero
 			if (step_up) {

src/collision.h

@@ -12,13 +12,13 @@ class IGameDef;
 class Environment;
 class ActiveObject;
 
-enum CollisionType
+enum CollisionType : u8
 {
 	COLLISION_NODE,
 	COLLISION_OBJECT,
 };
 
-enum CollisionAxis
+enum CollisionAxis : s8
 {
 	COLLISION_AXIS_NONE = -1,
 	COLLISION_AXIS_X,
@@ -37,9 +37,6 @@ struct CollisionInfo
 	v3f new_pos;
 	v3f old_speed;
 	v3f new_speed;
-
-	// FIXME: this is equivalent to `axis`, why does it exist?
-	int plane = -1;
 };
 
 struct collisionMoveResult