remove promise-polyfill (#9812)

promises are polyfilled by babel, it's no longer needed.

.ignore

@@ -1,5 +1,6 @@
 /vendor
-/public/vendor
+/public/vendor/plugins
+/public/vendor/assets
 /modules/options/bindata.go
 /modules/public/bindata.go
 /modules/templates/bindata.go

public/vendor/librejs.html

@@ -150,11 +150,6 @@
           <td><a href="https://github.com/moment/moment/blob/develop/LICENSE">MIT</a></td>
           <td><a href="https://github.com/moment/moment/archive/2.22.2.tar.gz">0.4.1.tar.gz</a></td>
         </tr>
-        <tr>
-          <td><a href="./plugins/promise-polyfill/">promise-polyfill</a></td>
-          <td><a href="https://github.com/taylorhakes/promise-polyfill/blob/master/LICENSE">MIT</a></td>
-          <td><a href="https://github.com/taylorhakes/promise-polyfill/archive/8.1.0.tar.gz">8.1.0.tar.gz</a></td>
-        </tr>
       </tbody>
     </table>
   </body>

templates/base/head.tmpl

@@ -126,7 +126,6 @@
 {{end}}
 	<style class="list-search-style"></style>
 
-	<script src="{{StaticUrlPrefix}}/vendor/plugins/promise-polyfill/polyfill.min.js"></script>
 	<script src="{{StaticUrlPrefix}}/vendor/plugins/cssrelpreload/loadCSS.min.js"></script>
 	<script src="{{StaticUrlPrefix}}/vendor/plugins/cssrelpreload/cssrelpreload.min.js"></script>
 {{if .PageIsUserProfile}}