This fixes the existing lowering of {JSGetSuperConstructor} nodes to
unconditional throws. The above operator is marked as {kNoWrite} but
runtime calls are not marked as such. Any deoptimizing operation after
the throw would not be able to find a valid {Checkpoint}. We remove the
lowering case in question.

R=bmeurer@chromium.org
TEST=mjsunit/regress/regress-6248
BUG=v8:6248

Change-Id: I22c922947336254502f698b02f944cf35dd8688a
Reviewed-on: https://chromium-review.googlesource.com/476570Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44632}