The templatized function body decoder already properly terminates
control flow, it is not needed for the graph building implementation to
do that explicitly upon {Throw} and {Rethrow}.

R=titzer@chromium.org
BUG=v8:8091

Change-Id: I47a93135c41b4cdf2fa6b8f5c7abfd6c212aaa12
Reviewed-on: https://chromium-review.googlesource.com/c/1273239
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56559}