Only initiate the WebSocket closing handshake on the client

#3342
Revert "Added test to verify that WindowsIdentities are usable in OnDisconnected"

This reverts commit e1b1de6f5f59aa2058a8795d3201230d00736ab9.
Revert "Stop processing messages before ending the WebSocketFunc Task"

This reverts commit 654bfb4198c7f20c49c068335c29d47c5011cb97.