Simplify findList and removeList in boards store

We don't really use the type argument and it also does not work
correctly.

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

@@ -242,7 +242,7 @@ export default {
         let toList;
         if (to) {
           const containerEl = to.closest('.js-board-list');
-          toList = boardsStore.findList('id', Number(containerEl.dataset.board), '');
+          toList = boardsStore.findList('id', Number(containerEl.dataset.board));
         }
 
         /**

app/assets/javascripts/boards/stores/boards_store.js

@@ -101,7 +101,7 @@ const boardsStore = {
   },
   new(listObj) {
     const list = this.addList(listObj);
-    const backlogList = this.findList('type', 'backlog', 'backlog');
+    const backlogList = this.findList('type', 'backlog');
 
     list
       .save()
@@ -185,8 +185,8 @@ const boardsStore = {
     return list.issues.find((issue) => issue.id === id);
   },
 
-  removeList(id, type = 'blank') {
-    const list = this.findList('id', id, type);
+  removeList(id) {
+    const list = this.findList('id', id);
 
     if (!list) return;
 
@@ -461,15 +461,8 @@ const boardsStore = {
       moveAfterId: afterId,
     });
   },
-  findList(key, val, type = 'label') {
-    const filteredList = this.state.lists.filter((list) => {
-      const byType = type
-        ? list.type === type || list.type === 'assignee' || list.type === 'milestone'
-        : true;
-
-      return list[key] === val && byType;
-    });
-    return filteredList[0];
+  findList(key, val) {
+    return this.state.lists.find((list) => list[key] === val);
   },
   findListByLabelId(id) {
     return this.state.lists.find((list) => list.type === 'label' && list.label.id === id);

ee/spec/frontend/boards/components/board_settings_wip_limit_spec.js

@@ -186,7 +186,7 @@ describe('BoardSettingsWipLimit', () => {
 
     afterEach(() => {
       flash.mockReset();
-      boardsStore.removeList(listId, 'label');
+      boardsStore.removeList(listId);
     });
 
     describe.each`

spec/frontend/boards/boards_store_spec.js

@@ -585,7 +585,7 @@ describe('boardsStore', () => {
 
         expect(boardsStore.state.lists.length).toBe(1);
 
-        boardsStore.removeList(listObj.id, 'label');
+        boardsStore.removeList(listObj.id);
 
         expect(boardsStore.state.lists.length).toBe(0);
       });