Removed Collections code from Admin

ref https://linear.app/ghost/issue/ENG-1805/remove-collections-code

- we're removing this feature as it's not finished to the degree we
  would like, so this commit removes all references to it from Admin in
  order to keep things clean

apps/admin-x-settings/src/components/settings/advanced/labs/AlphaFeatures.tsx

@@ -19,10 +19,6 @@ const features = [{
     title: 'Email customization',
     description: 'Adding more control over the newsletter template',
     flag: 'emailCustomization'
-},{
-    title: 'Collections',
-    description: 'Enables Collections 2.0',
-    flag: 'collections'
 },{
     title: 'Collections Card',
     description: 'Enables the Collections Card for pages - requires Collections and the beta Editor to be enabled',

ghost/admin/app/components/koenig-lexical-editor.js

@@ -1,7 +1,6 @@
 import * as Sentry from '@sentry/ember';
 import Component from '@glimmer/component';
 import React, {Suspense} from 'react';
-import fetch from 'fetch';
 import ghostPaths from 'ghost-admin/utils/ghost-paths';
 import moment from 'moment-timezone';
 import {action} from '@ember/object';
@@ -276,24 +275,6 @@ export default class KoenigLexicalEditor extends Component {
             return response;
         };
 
-        const fetchCollectionPosts = async (collectionSlug) => {
-            if (!this.contentKey) {
-                const integrations = await this.store.findAll('integration');
-                const contentIntegration = integrations.findBy('slug', 'ghost-core-content');
-                this.contentKey = contentIntegration?.contentKey.secret;
-            }
-
-            const postsUrl = new URL(this.ghostPaths.url.admin('/api/content/posts/'), window.location.origin);
-            postsUrl.searchParams.append('key', this.contentKey);
-            postsUrl.searchParams.append('collection', collectionSlug);
-            postsUrl.searchParams.append('limit', 12);
-
-            const response = await fetch(postsUrl.toString());
-            const {posts} = await response.json();
-
-            return posts;
-        };
-
         const fetchAutocompleteLinks = async () => {
             const defaults = [
                 {label: 'Homepage', value: window.location.origin + '/'},
@@ -455,13 +436,11 @@ export default class KoenigLexicalEditor extends Component {
             unsplash: this.settings.unsplash ? unsplashConfig.defaultHeaders : null,
             tenor: this.config.tenor?.googleApiKey ? this.config.tenor : null,
             fetchAutocompleteLinks,
-            fetchCollectionPosts,
             fetchEmbed,
             fetchLabels,
             renderLabels: !this.session.user.isContributor,
             feature: {
                 collectionsCard: this.feature.collectionsCard,
-                collections: this.feature.collections,
                 contentVisibility: this.feature.contentVisibility
             },
             deprecated: { // todo fix typo