Revert "[omnibox] Enable keyword search button by default."

This reverts commit 4ad67f3.

Reason for revert: We're holding off on rolling this out while we evaluate some changes to how triggering works.

Original change's description:
> [omnibox] Enable keyword search button by default.
>
> Also update unit tests to use Suggestion Button
> Row/Keyword Search Button test by default.
>
> Bug: 1046523
> Change-Id: Icbb41a9a10844b363d6d9fb89c401266b4858576
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2674166
> Commit-Queue: Angela Yoeurng <yoangela@chromium.org>
> Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#851918}

Bug: 1046523
Change-Id: I8b6796f8e466b823792999eb869dc20ca4c24bd1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2701652
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Justin Donnelly <jdonnelly@chromium.org>
Cr-Commit-Position: refs/heads/master@{#854975}

components/omnibox/browser/autocomplete_controller.h

@@ -211,6 +211,10 @@ class AutocompleteController : public AutocompleteProviderListener,
                            PopupStepSelectionWithHiddenGroupIds);
   FRIEND_TEST_ALL_PREFIXES(OmniboxPopupModelTest,
                            PopupInlineAutocompleteAndTemporaryText);
+  FRIEND_TEST_ALL_PREFIXES(OmniboxPopupModelSuggestionButtonRowTest,
+                           PopupStepSelectionWithButtonRow);
+  FRIEND_TEST_ALL_PREFIXES(OmniboxPopupModelSuggestionButtonRowTest,
+                           PopupStepSelectionWithButtonRowAndKeywordButton);
   FRIEND_TEST_ALL_PREFIXES(OmniboxPopupContentsViewTest,
                            EmitSelectedChildrenChangedAccessibilityEvent);