Revert "SplitSettings: Use assistant icon for assistant section"

This reverts commit fdbb564b.

Reason for revert: We're changing the section back to
"Search and assistant", so we're going back to the magnifying
glass icon.

Original change's description:
> SplitSettings: Use assistant icon for assistant section
>
> OS settings doesn't control search engine, so don't use a magnifying
> glass icon. Use the assistant icon instead.
>
> See bug for screenshot.
>
> Bug: 960937
> Change-Id: Icd2929a76572468df4d6615166c4b9d2782c4c36
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1674641
> Auto-Submit: James Cook <jamescook@chromium.org>
> Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
> Commit-Queue: James Cook <jamescook@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#671859}

TBR=jamescook@chromium.org,stevenjb@chromium.org

Bug: 960937
Change-Id: Ic99f8b98f2f782bdcb3535e35cd9158c06cc25ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1716915Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680483}

chrome/browser/resources/settings/chromeos/os_settings_menu/os_settings_menu.html

@@ -173,7 +173,7 @@
       <!-- TODO(jamescook): Rename path to "/assistant". -->
       <a href="/search" hidden="[[!showAssistant]]">
         <div class="item">
-          <iron-icon icon="settings:assistant"></iron-icon>
+          <iron-icon icon="cr:search"></iron-icon>
           $i18n{osAssistantPageTitle}
         </div>
       </a>

chrome/browser/resources/settings/icons.html

@@ -40,7 +40,6 @@ List icons here rather than importing large sets of (e.g. Polymer) icons.
 
 <if expr="chromeos">
       <!-- Icons from http://icons/ -->
-      <g id="assistant"><path d="M18.636 6.364a1.364 1.364 0 1 1 .001-2.729 1.364 1.364 0 0 1 0 2.729zm-4.09 4.545a2.727 2.727 0 1 1 0-5.454 2.727 2.727 0 0 1 0 5.454zm0 7.273a3.182 3.182 0 1 1 0-6.364 3.182 3.182 0 0 1 0 6.364zM10.908 5.455a5.455 5.455 0 1 1-10.91 0 5.455 5.455 0 0 1 10.91 0z"></path></g>
       <g id="play-prism"><path d="M20.18 10.88l-3.06-1.74L14.26 12l2.86 2.86 3.06-1.74c.55-.31.82-.71.82-1.12 0-.41-.27-.81-.82-1.12zM4.71 2.45l8.42 8.42 2.55-2.55-10.7-6.06c-.07-.04-.14-.07-.21-.1-.17-.07-.3.05-.15.21.03.02.06.05.09.08zm0 19.1l-.08.08c-.15.15-.02.28.15.21.07-.03.14-.06.21-.1l10.69-6.06-2.55-2.55s-7.2 7.21-8.42 8.42zM12 12L3.38 3.38c-.19-.19-.38-.07-.38.19v16.86c0 .26.19.38.38.19L12 12z"></path></g>
 
       <!-- Apps icon for Settings drawer -->