Revert "Merge branch 'js-i18n-board-store' into 'master'"

This reverts merge request !28712

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

-import { __ } from '~/locale';
-
 const notImplemented = () => {
-  throw new Error(__('Not implemented!'));
+  throw new Error('Not implemented!');
 };
 
 export default {

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

 import * as mutationTypes from './mutation_types';
-import { __ } from '~/locale';
 
 const notImplemented = () => {
-  throw new Error(__('Not implemented!'));
+  throw new Error('Not implemented!');
 };
 
 export default {

locale/gitlab.pot

@@ -6563,9 +6563,6 @@ msgstr ""
 msgid "Not found."
 msgstr ""
 
-msgid "Not implemented!"
-msgstr ""
-
 msgid "Not now"
 msgstr ""