The type guard should never be used after the effect/control
linearization pass, so making it a simplified operator better
expresses the intended use. Also this way none of the common
operators actually has any dependency on the type system.

Drive-by-fix: Properly print the type parameter to a TypeGuard operator.

BUG=chromium:612142
R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/1994503002
Cr-Commit-Position: refs/heads/master@{#36304}