Cleanup in code: removed unused directives

DocX/Charts/Axis.cs

 using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
 using System.Xml.Linq;
 
 namespace Novacode

DocX/Charts/Chart.cs

 using System;
 using System.Collections.Generic;
 using System.Linq;
-using System.Text;
 using System.Xml.Linq;
-using System.IO;
-using System.IO.Packaging;
 using System.Collections;
 using System.Drawing;
-using System.Reflection;
 
 namespace Novacode
 {

DocX/Charts/LineChart.cs

-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Xml.Linq;
+using System.Xml.Linq;
 
 namespace Novacode
 {

DocX/Charts/PieChart.cs

 using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
 using System.Xml.Linq;
 
 namespace Novacode