Removes EE differences for boards modal

app/assets/javascripts/boards/components/modal/footer.vue

 <script>
+import footerEEMixin from 'ee_else_ce/boards/mixins/modal_footer';
 import Flash from '../../../flash';
 import { __, n__ } from '../../../locale';
 import ListsDropdown from './lists_dropdown.vue';
@@ -10,7 +11,7 @@ export default {
   components: {
     ListsDropdown,
   },
-  mixins: [modalMixin],
+  mixins: [modalMixin, footerEEMixin],
   data() {
     return {
       modal: ModalStore.store,

app/assets/javascripts/boards/index.js

@@ -22,7 +22,7 @@ import '~/boards/filters/due_date_filters';
 import Board from 'ee_else_ce/boards/components/board';
 import BoardSidebar from 'ee_else_ce/boards/components/board_sidebar';
 import initNewListDropdown from 'ee_else_ce/boards/components/new_list_dropdown';
-import BoardAddIssuesModal from 'ee/boards/components/modal/index';
+import BoardAddIssuesModal from '~/boards/components/modal/index.vue';
 import '~/vue_shared/vue_resource_interceptor';
 import {
   NavigationType,

app/assets/javascripts/boards/mixins/modal_footer.js

+export default {};

ee/app/assets/javascripts/boards/components/modal/index.js

-import Vue from 'vue';
-import BoardAddIssuesModal from '~/boards/components/modal/index.vue';
-import ModalFooter from './footer';
-
-export default Vue.extend(BoardAddIssuesModal, {
-  components: {
-    ModalFooter,
-  },
-});

ee/app/assets/javascripts/boards/components/modal/footer.js → ee/app/assets/javascripts/boards/mixins/modal_footer.js

-import Vue from 'vue';
-import base from '~/boards/components/modal/footer.vue';
-
-export default Vue.extend(base, {
+export default {
   methods: {
     buildUpdateRequest(list) {
       const { currentBoard } = this.state;
@@ -16,4 +13,4 @@ export default Vue.extend(base, {
       };
     },
   },
-});
+};