[realbox] Move Header chevron from right side to directly adjacent

This is a follow-up to crrev.com/c/2404663
https://screenshot.googleplex.com/7sg94xt2F9CqNFb

Bug: 1127090
Change-Id: I523d509ff628071c436239ce61ce52c98d46ac95
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2411299
Commit-Queue: Tommy Li <tommycli@chromium.org>
Reviewed-by: Tommy Li <tommycli@chromium.org>
Auto-Submit: Moe Ahmadi <mahmadi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#807084}

chrome/browser/resources/new_tab_page/realbox_dropdown.html

@@ -23,7 +23,6 @@
   .header {
     align-items: center;
     display: flex;
-    justify-content: space-between;
     margin-top: 8px;
     outline: none;
     padding-bottom: 6px;