Remove the pre-C++17 implementation of void_t, just use std::void_t now.

R=omerkatz@chromium.org

Bug: v8:12425
Change-Id: Iabf72f1540ddb4db666e5a74f169f73546241c1f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3571888Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79812}