[iOS][PageInfo] Make UI flag enable/disable the master ATP feature

ATP fetching is only avaible if the master AboutThisPage feature is
enabled. This CL matches the state of the master ATP feature to the UI
feature flag.

Bug: none
Change-Id: I5a7da8166243f28ad4f52b621f03d18341a78dea
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5614690


Auto-Submit: Filipa Senra <fsenra@google.com>
Reviewed-by: Christian Dullweber <dullweber@chromium.org>
Commit-Queue: Filipa Senra <fsenra@google.com>
Commit-Queue: Christian Dullweber <dullweber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1312767}