removed unused namespace

Author: Petr Sramek

src/PolylineAlgorithm/Polyline.cs

@@ -4,7 +4,6 @@
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.InteropServices;
-using System.Runtime.Serialization;
 
 [StructLayout(LayoutKind.Auto)]
 [DebuggerDisplay("Value: {ToString()}, IsEmpty: {IsEmpty}, Length: {Length}")]