Migrate absl variant.h and utility.h in headless

Since https://crrev.com/c/6330348, some utils in
third_party/abseil-cpp/absl/types/variant.h and
and third_party/abseil-cpp/absl/utility/utility.h are only aliases for
their std counterparts. This CL migrates code to use std:: directly.

Bug: 40242126
Change-Id: I984f3312078a04090436b5237f2eb0d3a43fabbc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6343015
Reviewed-by: Eric Seckler <eseckler@chromium.org>
Commit-Queue: Victor Vianna <victorvianna@google.com>
Cr-Commit-Position: refs/heads/main@{#1430888}