NH-3700 - Remove un-needed System.CodeDom PackageReference.

Author: ngbrown

src/NHibernate/NHibernate.csproj

@@ -55,7 +55,6 @@
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
-    <PackageReference Include="System.CodeDom" Version="4.4.0" />
     <PackageReference Include="System.Configuration.ConfigurationManager" Version="4.4.0" />
     <PackageReference Include="System.Reflection.Emit" Version="4.3.0" />
     <PackageReference Include="System.Reflection.Emit.ILGeneration" Version="4.3.0" />