This reverts commit b1c1f6907fec2d18ae8b00ebc44975cb46a95b11.
Reason for revert: It may be the cause of iOS64 Debug flakyness.
Original change's description:
> Stop using and delete DEPRECATED_SingleThreadedTaskQueueForTesting
>
> Bug: webrtc:10933
> Change-Id: I8307e2aad06d3f3f367af122e43ecc088b52f2d6
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/157896
> Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
> Reviewed-by: Sebastian Jansson <srte@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#29713}
TBR=danilchap@webrtc.org,srte@webrtc.org
# Not skipping CQ checks because original CL landed > 1 day ago.
Bug: webrtc:10933
Change-Id: I94c86ebbae414a7569f253d199efbde6ac4c3765
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/159101
Reviewed-by: Honghai Zhang <honghaiz@webrtc.org>
Commit-Queue: Honghai Zhang <honghaiz@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29737}