[SHv2] Clean up unused site permissions module in site settings

This is part of the larger Safety Hub feature check clean up now that
Safety Hub is fully launched on desktop. The unused site permissions
module is now replaced by Safety Hub specific module, this changes
cleans up the dead code and obsolete metrics and strings.

OBSOLETE_HISTOGRAM[Settings.SafetyCheck.UnusedSitePermissionsListCount]=No longer logged

Bug: 40267370, 40880681, 40277421
Change-Id: I3f4af1fef2fb6bc23ef79dfeb4987b8298ea8b99
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6055401
Reviewed-by: Side YILMAZ <sideyilmaz@chromium.org>
Reviewed-by: Christian Dullweber <dullweber@chromium.org>
Commit-Queue: Zaina Al-Mashni <zalmashni@google.com>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1391004}