Removed unused code from SolarWinds.InformationService.Contract

[danjagnow]

Removed unused code from SolarWinds.InformationService.Contract.csproj:

• Removed unused SwisProxyBase abstract class
• Removed unused IInformationServiceChannel interface
• Removed several unused constructors and a CreateQuery overload from InformationServiceContext
• Removed an unused constructor from InformationServiceQuery
• Removed the EntityCollectionResponseParserType constant from InformationServiceQuery<T>
• Removed unused ErrorMessages property from ResponseParser and IResponseParser.
• Removed unused Deserialize and GetString methods from SerializationHelper.
• Removed unused EmptyCredentials class and static None property from the ServiceCredentials class
• Removed unused IIndicationReporter interface
• Removed unused IPersistentNotificationService interface
• Removed unused Subscription class
• Removed unused constructor and TryGetEntity and DescendantsOf methods from EntityClassGraph
• Removed unused MessageProperty constant
• Removed unused ReaderQuotaHelper class. Removed a reference to the corresponding namespace from InfoServiceProxy
• Removed unnecessary InternalsVisibleTo attribute from the AssemblyInfo.cs file for SolarWinds.InformationService.Contract.csproj.
• Removed unused ErrorMessages property from EntityCollectionResponseParser.