After the recent bugfix, the special case for 'undefined' is no longer
needed.

Bug: v8:7813
Change-Id: Iee3fccd72c525ac86a6fa6b3c55bcd2ce8159852
Reviewed-on: https://chromium-review.googlesource.com/1161906Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54897}