[NTP] Allow horizontal scrolling

When the browser is narrow or zoomed in allow a horizontal scrollbar
to appear.

Bug: 869196
Change-Id: Idefa746a8fa1e8ab4f263062c7703d1409c2c7b4
Reviewed-on: https://chromium-review.googlesource.com/1174970Reviewed-by: Kristi Park <kristipark@chromium.org>
Commit-Queue: Kyle Milka <kmilka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583096}

chrome/browser/resources/local_ntp/local_ntp.css

@@ -68,7 +68,6 @@ body {
   font-size: small;
   margin: 0;
   min-height: 100%;
-  overflow-x: hidden;
 }
 
 body.inited {