It was used only to break the circular dependency between SocketServer
and Thread at destruction time. Replaced with a method call to
SetMessageQueue(nullptr).
Bug: webrtc:11943
Change-Id: I0606d473ad79655cca28411bb02c21e21d2d7220
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/215587
Reviewed-by: Tommi <tommi@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33807}