[settings] Remove NoDestructor use from PrivacySection

Arrays of static data in static base::NoDestructor<std::vector<T>>
instances are wasteful; just make them plain old arrays that can live in
rodata.

This turns out to be a bit tricky, since there are quite a few search
concepts that are only conditionally included.
- For features that have been launched for some time, simply remove the
  feature checks.
- For functions that only conditionally include search concepts (e.g.
  search concepts that only make sense when not in guest mode), push the
  conditional check up into the caller.

Note: while feature values are generally fixed for the lifetime of a
program, and it should be "safe" to cache values calculated off feature
flags in static variables:
1. This is not true in tests.
2. It is an anti-pattern, since the general case (caching something
   dynamically calculated in a variable with static lifetime) is not
   always safe.

Bug: 341915558
Bug: 370837212
Bug: 375364966
Change-Id: I637f872aa31369ccd6d1ebe857214bf05e8101bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5984258
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Reviewed-by: Connie Xu <conniekxu@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1378688}