Cros: Remove shadow from enterprise-card

BUG=chromium:811556
TEST=manual

Change-Id: I1df22982da64bd19314b0c107a8342d4e9455169
Reviewed-on: https://chromium-review.googlesource.com/1221728Reviewed-by: Denis Kuznetsov <antrim@chromium.org>
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Commit-Queue: Roman Sorokin <rsorokin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590702}

chrome/browser/resources/chromeos/login/enterprise_card.css

@@ -36,7 +36,6 @@
 }
 
 .content-container {
-  box-shadow: 0 2px 2px 0 rgba(0, 0, 0, 0.17);
   padding: 0 64px 0 64px;
   z-index: 1;
 }