Replace dropdown promotions clear button FA icon with GlIcon close

Also removed unnecessary margin rule which threw everything out

ee/app/assets/stylesheets/pages/promotions.scss

@@ -153,7 +153,6 @@
   }
 
   .dropdown-title {
-    margin: 0 -25px;
     padding: 0;
     overflow: initial;
     border-bottom: 0;

ee/app/views/shared/promotions/_promote_epics.html.haml

@@ -11,11 +11,11 @@
       = _('Epic')
     .dropdown
       .dropdown-menu.promotion-issue-sidebar-message
-        .dropdown-title
-          %span
+        .dropdown-title.gl-display-flex
+          %span.gl-ml-auto
             = _('Epic')
-          %button.dropdown-title-button.dropdown-menu-close{ "aria-label" => _('Close'), :type => "button" }
-            %i.fa.fa-times.dropdown-menu-close-icon{ "aria-hidden" => "true", "data-hidden" => "true" }
+          %button.dropdown-title-button.dropdown-menu-close.gl-ml-auto{ "aria-label" => _('Close'), :type => "button" }
+            = sprite_icon('close', size: 16, css_class: 'dropdown-menu-close-icon')
         %div
           %p
             = s_('Promotions|Epics let you manage your portfolio of projects more efficiently and with less effort by tracking groups of issues that share a theme, across projects and milestones.')

ee/app/views/shared/promotions/_promote_issue_templates.html.haml

@@ -4,9 +4,9 @@
   = _('to help your contributors communicate effectively!')
   .dropdown.promotion-issue-template
     .dropdown-menu.promotion-issue-template-message
-      .dropdown-title
+      .dropdown-title.gl-display-flex.gl-justify-content-end
         %button.dropdown-title-button.dropdown-menu-close{ "aria-label" => "Close", :type => "button" }
-          %i.fa.fa-times.dropdown-menu-close-icon{ "aria-hidden" => "true", "data-hidden" => "true" }
+          = sprite_icon('close', size: 16, css_class: 'dropdown-menu-close-icon')
       %div
         %p
           = _('Description templates allow you to define context-specific templates for issue and merge request description fields for your project.')