Remove search companion WebUI.

Cq-Include-Trybots: luci.chrome.try:linux-chromeos-chrome,mac-chrome
Bug: b:273782868
Change-Id: I55633453fb0fd94db0b9d641cf9c85ca5c7a8383
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4348157


Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Thomas Lukaszewicz <tluk@chromium.org>
Commit-Queue: Juan Mojica <juanmojica@google.com>
Reviewed-by: Matthew Denton <mpdenton@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1118446}