Since the comments are copied from the std types anyway, we should also
point to them to make clear that the semantic is intentially equivalent.

Also, remove two unused methods and avoid an unneeded nullptr check.

R=mlippautz@chromium.org

Bug: v8:8834
Change-Id: Idcb5a1b8b2b3bb0786807828a96e085df963a8f0
Reviewed-on: https://chromium-review.googlesource.com/c/1477224Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59692}