This reverts commit ff77c359.

Reason for revert: Breaks FramebufferMixedSamplesTest on Android NVIDIA

BUG=angleproject:2045

Original change's description:
> Refactor multisample framebuffer completeness checks.
> 
> BUG=722684
> 
> Change-Id: Iebe6968ebd693e7f051394a040eac1cf6f539e6e
> Reviewed-on: https://chromium-review.googlesource.com/508221
> Reviewed-by: Geoff Lang <geofflang@chromium.org>
> Reviewed-by: Jamie Madill <jmadill@chromium.org>
> Commit-Queue: Geoff Lang <geofflang@chromium.org>
> 

TBR=fjhenigman@chromium.org,geofflang@chromium.org,jmadill@chromium.org
# Not skipping CQ checks because original CL landed > 1 day ago.
BUG=722684

Change-Id: I1abab021ba73b218cbbe60d4e7bfdaae56955c64
Reviewed-on: https://chromium-review.googlesource.com/517390Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>