Do not apply HTTP flags if telemetry is disabled

Blindly pushing flags to apps that cannot tell us if something regresses
doesn't seem like the best idea. We keep an override around if for
whatever reason we want to do it anyway (e.g. emergencies).

Bug: b:430895740
Want-Code-Review: all
Change-Id: I7ff68b9da1d9aa756a1d67ee299072bd5c451493
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6734446
Reviewed-by: Stefano Duo <stefanoduo@google.com>
Commit-Queue: Etienne Dechamps <edechamps@google.com>
Reviewed-by: Mohannad Farrag <aymanm@google.com>
Cr-Commit-Position: refs/heads/main@{#1487038}