Remove C++17 canary

I had added a small snippet of no-op code here to make sure
this file builds in C++17 everywhere.

By now, C++17 is enabled and we use `if constexpr` in many
other places in base/, so remove that snippet again.

Bug: 752720
Change-Id: I5a10d515b43a65710a0bea132ede681313dda3b9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3383435


Commit-Queue: Nico Weber <thakis@chromium.org>
Auto-Submit: Nico Weber <thakis@chromium.org>
Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/main@{#958145}