Update 'src/app/components/middle-point/models/middle-point-model.js'

Fixes to read GEO file with midpoint.
To export GEO file with midpoint, fixed "static do (map, list)".
Removed reference to "old" variable/object "pointC":
- from: return new MiddlePointModel(pointA, pointB, pointC, label, id);
- to:  return new MiddlePointModel(pointA, pointB, label, id);

src/app/components/middle-point/models/middle-point-model.js

@@ -59,7 +59,7 @@ export class MiddlePointModel extends PointModel {
     const pointA = list.find(x => x.id === pointAId);
     const pointB = list.find(x => x.id === pointBId);
     const label = map.get("label")[0];
-    return new MiddlePointModel(pointA, pointB, pointC, label, id);
+    return new MiddlePointModel(pointA, pointB, label, id);
     }
 
   }