[CodeHealth] Remove stale base::Feature EnableLocalSearchService

Enabled by default since M89.

Bug: 356234181
Change-Id: I612166b08a42302e13579b5c07fe5e7706d14bc5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5983187


Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Reviewed-by: Thanh Nguyen <thanhdng@chromium.org>
Reviewed-by: Zufeng Wang <zufeng@google.com>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1378893}