Chrome OS OOBE: add floating bottom-border to the network selection.

Bottom-botder was disabled (because it conflicted with another line).
This Cl returns it back.

Bug: 852049
Change-Id: I2bd0d2282114809f19e85bced6f821b1b8379aa7
Reviewed-on: https://chromium-review.googlesource.com/1171954Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Alexander Alekseev <alemate@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583160}

chrome/browser/resources/chromeos/login/oobe_network.html

@@ -19,7 +19,7 @@
       </div>
       <div slot="footer" class="layout vertical">
         <network-select-login id="networkSelectLogin"
-            is-connected="{{isConnected_}}" no-bottom-scroll-border>
+            is-connected="{{isConnected_}}">
         </network-select-login>
       </div>
       <div slot="bottom-buttons" class="layout horizontal justified">