Revert "Finish ReadBuffer support in end2end_tests." Fails on the bots, on ReadPixelsTest.DrawWithPBO/ES3_D3D11 BUG=angleproject:940 This reverts commit ada5d07ec6c3578eb07adbb647360c0ae60edf46. Change-Id: I60c71af6317f6b5ee1bf1555cb4573c5e82a11d6 Reviewed-on: https://chromium-review.googlesource.com/317430 Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>