Fixed build warning in UnitsNet.Tests.net35.csproj after downgrading to .NET 3.5 Client.

Microsoft.CSharp is missing.

Author: angularsen

Tests/UnitsNet.Tests.net35.csproj

@@ -40,7 +40,6 @@
     <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.Xml" />
   </ItemGroup>