Revert of Improve tracking of bound FBOs in GrGLGpu. (patchset #10 id:180001 of https...

Revert of Improve tracking of bound FBOs in GrGLGpu. (patchset #10 id:180001 of https://codereview.chromium.org/949263002/)

Reason for revert:
Experimentally reverting to see if this is the cause of the mac_chromium_rel_ng roll-blocking failures.

Original issue's description:
> Improve tracking of bound FBOs in GrGLGpu.
>
> Committed: https://skia.googlesource.com/skia/+/d2ad8eb5801e2c8c0fa544a6a776bb46eedde2a0
>
> Committed: https://skia.googlesource.com/skia/+/b2af2d8b83ca4774c3b3bb1e49bc72605faa9589
>
> Committed: https://skia.googlesource.com/skia/+/0b70b86a7e9fda52ee7ebc1b9897eeaa09b9abef

TBR=egdaniel@google.com,bsalomon@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/970613003