GitLab

- Fix UA string not to report Fuchsia as an X11 platform.
- Switch Fuchsia away from using the generic POSIX OS & CPU info logic,
  with the result that CPU architecture is no longer reported.

Bug: 936327
Change-Id: I691253d4f83457a68fcd5d2ce5e5efdf47834381
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1639741
Commit-Queue: Wez <wez@chromium.org>
Auto-Submit: Wez <wez@chromium.org>
Reviewed-by: Thiemo Nagel <tnagel@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#666015}