Refactor and/or remove dead code in channel factory async close path

[roncain]

PR #1071 made the channel factory async close path remain async. This appears to have made the synchronous code path unreachable, because the low level IAsyncCommunicationObject logic uses the async close path even for sync closes

To resolve this issue:

• Establish via code coverage and analysis that the TypedServiceChannelFactory and ServiceChannelFactory OnClose and BeginClose have become unreachable
• Remove what can be removed or refactor to use common code path

[roncain]

It appears ServiceChannelManager.AddIncomingChannel is now dead code and can be removed. This is also reflected in areas in LifeTimeManager and ChannelCollection that are either not covered by tests or are now dead code. Investigate and remove if possible.

[roncain]

This is purely a cleanup task to remove dead code. I believe we have finished refactoring all the WCF product types derived from CommunicationObject to be entirely task-based. And this appears to have made many of the Begin/End methods dead. We also now have unit tests that verify custom channels and custom channel factories (that are unaware of the new Task API's) work properly without using the apparently dead Begin/End methods. Once the dead code has been removed, I believe this will orphan many AsyncResult derived types that can also be removed.