The emulation is already toggled by a compilation flag, so having it
behind an ifdef only adds unnecessary complexity, particularly when
testing changes to the emulation code.

BUG=angleproject:865

Change-Id: Idf7854c2b5323609880b527ed806440dcc8ac091
Reviewed-on: https://chromium-review.googlesource.com/256365Tested-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>