Remove duplicate nuget packages in SharpPcap csproj (#515)

* Remove duplicate nuget packages in SharpPcap csproj

* Address accidental deletion of 8.x CodePages nuget and remove 6.x

Author: kylejuliandev

Diff for: SharpPcap/SharpPcap.csproj

@@ -31,10 +31,8 @@ SPDX-License-Identifier: MIT
   <ItemGroup>
     <PackageReference Include="PacketDotNet" Version="1.4.7" />
     <PackageReference Include="System.Memory" Version="4.5.5" />
-    <PackageReference Include="System.Text.Encoding.CodePages" Version="6.0.0" />
-    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="8.0.0" PrivateAssets="All"/>
-    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="8.0.0" PrivateAssets="All"/>
     <PackageReference Include="System.Text.Encoding.CodePages" Version="8.0.0" />
+    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="8.0.0" PrivateAssets="All"/>
   </ItemGroup>
   <ItemGroup>
     <AssemblyAttribute Include="System.Runtime.CompilerServices.InternalsVisibleTo">