[Streaming] Remove unnecessary methods and properties from botframework-streaming

[stevengum]

Versions

botframework-streaming@4.6.0-preview3 via MyGet

Describe the bug

There are classes implementing interfaces where the methods implemented could be getters. Some of the methods on the interfaces may also be unneeded and could be removed.

ITransport which is impelmented by the NamedPipeTransport and WebSocketTransport denotes that isConnected(): boolean be implemented.

Searching the repository for references to ITransport.isConnected() beyond those three structs yields nothing, so the method should be removed.

Expected behavior

Necessary methods and properties should indicate what they're used for via their documentation, implementation and usage.

[bug]

[stevengum]

Created due to #1425