Move shortcut handles to `shortcuts_epic.js`

ee/app/assets/javascripts/epics/epic_show/sidebar_context.js

 import $ from 'jquery';
-import Mousetrap from 'mousetrap';
 import Cookies from 'js-cookie';
 import bp from '~/breakpoints';
 
@@ -7,10 +6,6 @@ export default class SidebarContext {
   constructor() {
     const $issuableSidebar = $('.js-issuable-update');
 
-    Mousetrap.bind('l', () =>
-      SidebarContext.openSidebarDropdown($issuableSidebar.find('.js-labels-block')),
-    );
-
     $issuableSidebar
       .off('click', '.js-sidebar-dropdown-toggle')
       .on('click', '.js-sidebar-dropdown-toggle', function onClickEdit(e) {
@@ -46,8 +41,4 @@ export default class SidebarContext {
       }
     });
   }
-
-  static openSidebarDropdown($block) {
-    $block.find('.js-sidebar-dropdown-toggle').trigger('click');
-  }
 }