Remove multi_select_board feature flag

Remove multi_select_board feature flag from FE and BE

app/assets/javascripts/boards/components/board_card_layout.vue

@@ -44,9 +44,6 @@ export default {
     multiSelectVisible() {
       return this.multiSelect.list.findIndex(issue => issue.id === this.issue.id) > -1;
     },
-    canMultiSelect() {
-      return gon.features && gon.features.multiSelectBoard;
-    },
   },
   methods: {
     mouseDown() {
@@ -59,7 +56,7 @@ export default {
       // Don't do anything if this happened on a no trigger element
       if (e.target.classList.contains('js-no-trigger')) return;
 
-      const isMultiSelect = this.canMultiSelect && (e.ctrlKey || e.metaKey);
+      const isMultiSelect = e.ctrlKey || e.metaKey;
 
       if (this.showDetail || isMultiSelect) {
         this.showDetail = false;

app/assets/javascripts/boards/components/board_list.vue

@@ -16,9 +16,7 @@ import {
 
 // This component is being replaced in favor of './board_list_new.vue' for GraphQL boards
 
-if (gon.features && gon.features.multiSelectBoard) {
-  Sortable.mount(new MultiDrag());
-}
+Sortable.mount(new MultiDrag());
 
 export default {
   name: 'BoardList',
@@ -100,12 +98,11 @@ export default {
   mounted() {
     // TODO: Use Draggable in ./board_list_new.vue to drag & drop issue
     // https://gitlab.com/gitlab-org/gitlab/-/issues/218164
-    const multiSelectOpts = {};
-    if (gon.features && gon.features.multiSelectBoard) {
-      multiSelectOpts.multiDrag = true;
-      multiSelectOpts.selectedClass = 'js-multi-select';
-      multiSelectOpts.animation = 500;
-    }
+    const multiSelectOpts = {
+      multiDrag : true,
+      selectedClass : 'js-multi-select',
+      animation : 500,
+    };
 
     const options = getBoardSortableDefaultOptions({
       scroll: true,

app/controllers/groups/boards_controller.rb

@@ -7,7 +7,6 @@ class Groups::BoardsController < Groups::ApplicationController
   before_action :authorize_read_board!, only: [:index, :show]
   before_action :assign_endpoint_vars
   before_action do
-    push_frontend_feature_flag(:multi_select_board, default_enabled: true)
     push_frontend_feature_flag(:graphql_board_lists, group, default_enabled: false)
     push_frontend_feature_flag(:boards_with_swimlanes, group, default_enabled: false)
   end

app/controllers/projects/boards_controller.rb

@@ -8,7 +8,6 @@ class Projects::BoardsController < Projects::ApplicationController
   before_action :authorize_read_board!, only: [:index, :show]
   before_action :assign_endpoint_vars
   before_action do
-    push_frontend_feature_flag(:multi_select_board, default_enabled: true)
     push_frontend_feature_flag(:boards_with_swimlanes, project, default_enabled: false)
   end