The code is a lot simpler when the type information is only carried
in the TType of the node, instead of being partially duplicated in the
enum value.

BUG=angleproject:1490
TEST=angle_unittests

Change-Id: I956376225ec01e469c7afb7378fa48cc097c0cea
Reviewed-on: https://chromium-review.googlesource.com/498768
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>