This specifier is deprecated and will be removed in C++20. Replace it
with V8_NOEXCEPT where is makes sense and remove it otherwise. Also
remove redundant constructors.

R=tebbi@chromium.org

Bug: v8:8562
Change-Id: I1335dcac5cac14b62b655cfd507decd4de653043
Reviewed-on: https://chromium-review.googlesource.com/c/1392204Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58517}