Revert of gpu: Add GL_TEXTURE_RECTANGLE_ARB support to CopyTexSubImage2D optimization of CopyTexture.

Revert of gpu: Add GL_TEXTURE_RECTANGLE_ARB support to CopyTexSubImage2D optimization of CopyTexture. (patchset #1 id:1 of https://codereview.chromium.org/1149233005/)

Reason for revert:
May have caused WebGL conformance test failures on OS X; see http://crbug.com/486922 .

Original issue's description:
> gpu: Add GL_TEXTURE_RECTANGLE_ARB support to CopyTexSubImage2D optimization of CopyTexture.
>
> The availability of this extension is already limited to desktop core
> profile as the only reason we need to support it is IOSurfaces on
> MacOSX.
>
> This provides 2x performance improvement of copy operations when using
> IOSurface backed GpuMemoryBuffers.
>
> BUG=486922
>
> Committed: https://crrev.com/48514369cc66bc04ec766adf774de41d396a33ad
> Cr-Commit-Position: refs/heads/master@{#333159}

TBR=piman@chromium.org,dongseong.hwang@intel.com,reveman@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=486922
Committed: https://crrev.com/0e8e291d8796a70363c50a11bdef62d1a7e5550e
Cr-Commit-Position: refs/heads/master@{#333187}

[Ken Russell (switch to Gerrit), 2015-06-06 00:35:52]

Created Revert of gpu: Add GL_TEXTURE_RECTANGLE_ARB support to CopyTexSubImage2D
optimization of CopyTexture.