Revert of Caching the result of readPixelsSupported (https://codereview.chromium.org/364193004/)

Reason for revert:
appears to crash GM on Ubuntu and Win8

http://108.170.220.120:10117/builders/Test-Ubuntu12-ShuttleA-GTX660-x86-Release/builds/1237/steps/GenerateGMs/logs/stdio

Original issue's description:
> Caching the result of readPixelsSupported
>
> The call was calling GR_GL_GetIntegerv 2 times for each readPixels
> and thus was causing a loss of performance
>
> (resubmit of issue 344793008)
>
> Benchmark url: http://packages.gkny.fr/tst/index.html
>
> BUG=skia:2681
>
> Committed: https://skia.googlesource.com/skia/+/753a2964afe5661ce9b2a8ca77ca9d0aabd3173c

R=junov@chromium.org, piotaixr@chromium.org
TBR=junov@chromium.org, piotaixr@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=skia:2681

Author: reed@chromium.org

Review URL: https://codereview.chromium.org/367323003
3 files changed