Revert "Add a close box to flights-app toast."

This reverts commit ffcbc3b2f5417b09328eae4aeb8de2e5eab6324d.

This test broke sky_tests:

Regressions: Unexpected text-only failures (6)
  framework/flights-app.sky [ Failure ]

Example:

http://build.chromium.org/p/client.mojo/builders/Mojo%20Linux%20ASan%20%28dbg%29/builds/173/steps/Sky%20tests/logs/stdio

TBR=ojan

Review URL: https://codereview.chromium.org/880863002

examples/flights-app/app-toast.sky

@@ -23,16 +23,6 @@
       flex-shrink: 0;
       margin-right: 6px;
     }
-
-    .close-box {
-      position: absolute;
-      top: 3px;
-      right: 3px;
-      width: 1em;
-      overflow: hidden;
-      text-align: center;
-      outline: 1px solid #AEA477;
-    }
   </style>
   <div class="header">
     <content select=".toast-icon" />
@@ -40,9 +30,6 @@
   <div class="content">
     <content select=".toast-content" />
   </div>
-  <div class="close-box">
-   X
-  </div>
 </template>
 <script>
 module.exports = class extends SkyElement {