Making them private was a way to hide them, we can explicitly delete
them, which give a better compilation error message as well.

Also see: https://stackoverflow.com/q/55205874

Bug: v8:10488
Change-Id: Ieffa05951aeefc0225f8fb84e756eb67353e57a3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2211184Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67982}