Revert of Improve tracking of bound FBOs in GrGLGpu.

Revert of Improve tracking of bound FBOs in GrGLGpu. (patchset #16 id:300001 of https://codereview.chromium.org/949263002/)

Reason for revert:
locally hit assert.

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
> 
> Committed: https://skia.googlesource.com/skia/+/6ba6fa15261be591f33cf0e5df7134e4fc6432ac
> 
> Committed: https://skia.googlesource.com/skia/+/dc963b9264908f53650c40a97cff414101dd3e88

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

Committed: https://skia.googlesource.com/skia/+/5cd020f27b79ab6efc411b08883d4108868d81e9

[bsalomon, 2015-03-17 19:46:32]

Created Revert of Improve tracking of bound FBOs in GrGLGpu.

[commit-bot: I haz the power, 2015-03-17 19:46:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1017803002/1

[commit-bot: I haz the power, 2015-03-17 19:47:00]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/5cd020f27b79ab6efc411b08883d4108868d81e9