[DIPS] Extends privacy.dips.deletion UMA for empty site(s)

Bug: 1447038
Change-Id: I428924b40cb014b8ca0ddaa252c87313fdf278bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4549637


Auto-Submit: Jonathan Njeunje <njeunje@chromium.org>
Reviewed-by: Ben Kelly <wanderview@chromium.org>
Commit-Queue: Ben Kelly <wanderview@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1146685}