Revert "Exercise the threaded backend in test bots"

This reverts commit a39991ebd70f4aaf1290dd516467d729811e45ee.

Reason for revert: Random bots timeout

Original change's description:
> Exercise the threaded backend in test bots
> 
> We can't draw everything correctly now, but it's at least not crashing.
> 
> The draw_to_canvas is modified by adding flush because now the raster
> canvas also needs flush like GPU canvases because of the threaded
> backend. (Previously, AndroidCodecSrc vetoed GPU (non-raster) sink
> and that's why it was not crashing.)
> 
> 
> Bug: skia:
> Change-Id: I222d706c33e15326e1b97d6bef6c46b8c35cebfd
> Reviewed-on: https://skia-review.googlesource.com/118886
> Reviewed-by: Kevin Lubick <kjlubick@google.com>
> Commit-Queue: Yuqian Li <liyuqian@google.com>

TBR=kjlubick@google.com,stephana@google.com,liyuqian@google.com

Change-Id: Ib1089d937b6e25cc39d90ad4de35b3a4c406f6b1
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:
Reviewed-on: https://skia-review.googlesource.com/119100
Reviewed-by: Yuqian Li <liyuqian@google.com>
Commit-Queue: Yuqian Li <liyuqian@google.com>
15 files changed