Revert 8273 "Temporarily change ThreadPosix to CHECK (crash) if ..."
Revert 8273 "Temporarily change ThreadPosix to CHECK (crash) if ..."

> Temporarily change ThreadPosix to CHECK (crash) if we ever spend more than 30 seconds waiting for thread shutdown. There are cases on build bots where it looks like we're hitting this problem, but reproducing locally has been a struggle.
> 
> TBR=pbos@webrtc.org
> 
> Review URL: https://webrtc-codereview.appspot.com/41799004

TBR=tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/38039004

git-svn-id: 03ae4fbe531b1eefc9d815f31e49022782c42458@8300 4adac7df-926f-26a2-2b94-8c16560cd09d

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