Revert "Improve ChromeVox continuous read"

This reverts commit 743f4e9d.

In extended usage, this doesn't work well for long text blocks. Stopping speech, ChromeVox is immediately brought to the end of that entire block. We need timepointing from tts to help here.

TBR=dtseng@chromium.org

Change-Id: I6fe2503618fefe35d9043453c56edfa4c05e9653
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2493121


Reviewed-by: David Tseng <dtseng@chromium.org>
Commit-Queue: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820055}