Don't reference System.ServiceModel in the client

It no longer seems necessary with .NEt 4.0+ and makes
it possible to use the client in SQL CLR (well, with
a couple of small tweaks to follow).

Author: michaelklishin

projects/client/RabbitMQ.Client/RabbitMQ.Client.csproj

@@ -264,7 +264,6 @@
     <Reference Include="System.Xml" />
     <Reference Include="System.Xml.Linq" />
     <Reference Include="System.Configuration" />
-    <Reference Include="System.ServiceModel" />
   </ItemGroup>
   <!-- Mono compatibility workarounds -->
   <PropertyGroup Condition=" '$(PropUsingMono)' == 'true'">