Update minimum non-ES OpenGL spec to 2.0.

Update minimum non-ES OpenGL spec to 2.0.

As a consequence of removing support for GLs lacking separate stencil settings our effective minimum GL version is 2.0. This formalizes that by explicitly failing if the version in the version string is lower.

As a consequence we will always have wrapping stencil operations available.
Bug: skia:
Change-Id: Ibe302f72a063dbadc773bda811cc0d0f6c08c61a
Reviewed-on: https://skia-review.googlesource.com/15610
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>