MD Settings: Remove unnecessary scrollbar from Sign out dialog.

BUG=632575
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2196613003
Cr-Commit-Position: refs/heads/master@{#408842}

chrome/browser/resources/settings/people_page/people_page.html

@@ -67,6 +67,10 @@
         height: var(--iron-icon-height);
         width: var(--iron-icon-width);
       }
+
+      paper-checkbox {
+        margin: 16px 0 2px;
+      }
     </style>
     <settings-animated-pages id="pages" current-route="{{currentRoute}}"
         section="people">