2D multisample is out of scope since its ES 3 only.

Bug: angleproject:2499
Change-Id: Id5f81d713a2882ba2a91b7d3f281d71a3e9289f4
Reviewed-on: https://chromium-review.googlesource.com/1046786
Commit-Queue: Luc Ferron <lucferron@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>