fixed unused namespaces that were no longer included failing the build

Author: Mpdreamz

src/CodeGeneration/Nest.Litterateur/Documentation/Files/CSharpDocumentationFile.cs

@@ -3,7 +3,6 @@
 using System.Linq;
 using System.Text;
 using Microsoft.CodeAnalysis.CSharp;
-using Microsoft.CodeAnalysis.Formatting;
 using Nest.Litterateur.Documentation.Blocks;
 using Nest.Litterateur.Walkers;
 

src/CodeGeneration/Nest.Litterateur/Walkers/CodeWithDocumentationWalker.cs

@@ -7,11 +7,6 @@
 using System.Linq;
 using System.Text;
 using System.Text.RegularExpressions;
-using Microsoft.CodeAnalysis.Formatting;
-#if !DOTNETCORE
-using Microsoft.CodeAnalysis.MSBuild;
-#endif
-using Microsoft.CodeAnalysis.Text;
 using Nest.Litterateur.Documentation.Blocks;
 
 namespace Nest.Litterateur.Walkers