refactor: remove UsableRemnantArea from NestProgress and UI

OpenNest.Engine/NestEngineBase.cs

@@ -229,7 +229,6 @@ namespace OpenNest
                 NestedWidth = bounds.Width,
                 NestedLength = bounds.Length,
                 NestedArea = totalPartArea,
-                UsableRemnantArea = workArea.Area() - totalPartArea,
                 BestParts = clonedParts,
                 Description = description
             });

OpenNest.Engine/NestProgress.cs

@@ -41,7 +41,6 @@ namespace OpenNest
         public double NestedWidth { get; set; }
         public double NestedLength { get; set; }
         public double NestedArea { get; set; }
-        public double UsableRemnantArea { get; set; }
         public List<Part> BestParts { get; set; }
         public string Description { get; set; }
     }