Revert "Fix check in GrGLGpu for whether PBO 0 is bound"

This reverts commit 62d42db2829d8f679afdb4fcfbbd7fc2948fea23.

Reason for revert: d3d9 angle tests failing

Original change's description:
> Fix check in GrGLGpu for whether PBO 0 is bound
>
> Found in OOP-R canvas in Chrome. Most likely async read followed by
> sync read with an intervening resetContext().
>
> Bug: chromium:1208212
>
> Change-Id: Ibf85f070d0a4cd389f67e9b249655b0ef667c66e
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/435277
> Commit-Queue: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Robert Phillips <robertphillips@google.com>
> Auto-Submit: Brian Salomon <bsalomon@google.com>
> Reviewed-by: Robert Phillips <robertphillips@google.com>
> Reviewed-by: John Stiles <johnstiles@google.com>

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: chromium:1208212
Change-Id: I85c89a4d0dd63aaafd80d7572c5643cfa547498b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/435617
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
2 files changed