Tab Search: Temporarily hide the close tab icon

This CL temporarily hides the close tab icon given the close tab
functionality has not yet been fully plumbed in.

This change will help avoid confusion when enabling Tab Search for
early users looking to give feedback.

Bug: 1099917
Change-Id: Ieed4c7d4220bb2edd07c0056198ac7d8490cb15f
Reviewed-on: https://chrome-internal-review.googlesource.com/c/chrome/browser/resources/tab_search/+/3204546Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819579}

chrome/browser/resources/tab_search_merge/tab_search_item.html

@@ -13,10 +13,6 @@
     background-color: rgba(var(--google-grey-900-rgb), 0.1);
   }
 
-  :host-context(.selected, :host:hover) .button-container {
-    display: flex;
-  }
-
   .button-container {
     display: none;
   }