This reverts commit 92049513.

Reason for revert: crbug.com/1186140

Original change's description:
> Fix bindFramebuffer problem with GLES2 devices
>
> GLES2 and OpengGL 2 don't support GL_{DRAW,READ}_FRAMEBUFFER.
> Always uses GL_FRAMEBUFFER for them.
>
> Bug: chromium:1167731
> Change-Id: Iab75a27b4c47d0bdaa2ec18a9019fd2d2535b04d
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2737062
> Commit-Queue: Peng Huang <penghuang@chromium.org>
> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
> Reviewed-by: Geoff Lang <geofflang@chromium.org>

Bug: chromium:1167731, chromium:1186140
Change-Id: I1425bc9cf4145887193b7d18f956d6fbf07ce028
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2743661
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Peng Huang <penghuang@chromium.org>