[RDSC] Request Desktop Site IPH post-launch cleanup

OBSOLETE_HISTOGRAMS=The histograms in-built in the feature engagement system and associated with the "specific"/arm 1 (for top domains) RDS per-site IPH are no longer required because this IPH is not going to be launched.

Bug: 1459063
Change-Id: Id6e2c9fb9ba2d13da6a8d97b7868b6f0c6254950
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4679461
Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
Reviewed-by: Sirisha Kavuluru <skavuluru@google.com>
Commit-Queue: Aishwarya Rajesh <aishwaryarj@google.com>
Reviewed-by: Theresa Sullivan <twellington@chromium.org>
Code-Coverage: Findit <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1172083}