Remove availability attribute from a few places as a workaround.

-Wunguarded-availability now applies to template instantiations.
Temporarily remove the attribute from places where the warning fires.

Bug: 345303691
Change-Id: If4f71d00d40aa9bac6dc858e31fbc75fdd8feaf9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5609500


Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Amy Huang <akhuang@google.com>
Reviewed-by: Frank Liberato <liberato@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1313017}