Refactor settings_reset_prompt to use PrefService::GetValueList

This is part of a larger migration effort based on
go/trust-your-prefs.

Bug: 1341998
Test: Adjusted browser test
Change-Id: Ic1e6edab1a639f88478246170122a16eea5f13f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3870505


Reviewed-by: Daniel Rubery <drubery@chromium.org>
Commit-Queue: Roland Bock <rbock@google.com>
Cr-Commit-Position: refs/heads/main@{#1042723}