remove references

Mono.Nat/Mono.Nat.csproj

@@ -33,11 +33,7 @@
   <ItemGroup>
     <Reference Include="System" />
     <Reference Include="System.Core" />
-    <Reference Include="System.Xml.Linq" />
-    <Reference Include="System.Data.DataSetExtensions" />
     <Reference Include="Microsoft.CSharp" />
-    <Reference Include="System.Data" />
-    <Reference Include="System.Net.Http" />
     <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>