enabled always sending mentions (#16227)

refs TryGhost/Team#2507
-removed labs check from sending service
-labs flag controls seeing mentions in admin and receiving mentions

ghost/admin/app/templates/settings/labs.hbs

@@ -218,7 +218,7 @@
                         <div>
                             <h4 class="gh-expandable-title">Webmentions</h4>
                             <p class="gh-expandable-description">
-                                Allow receiving webmentions from external sites and sending webmentions when linking external sites in posts.
+                                Allows receiving webmentions from external sites and viewing them on the dashboard.
                             </p>
                         </div>
                         <div class="for-switch">

ghost/core/core/server/services/mentions/service.js

@@ -13,7 +13,6 @@ const events = require('../../lib/common/events');
 const externalRequest = require('../../../server/lib/request-external.js');
 const urlUtils = require('../../../shared/url-utils');
 const outputSerializerUrlUtil = require('../../../server/api/endpoints/utils/serializers/output/utils/url');
-const labs = require('../../../shared/labs');
 const urlService = require('../url');
 const settingsCache = require('../../../shared/settings-cache');
 const DomainEvents = require('@tryghost/domain-events');
@@ -89,7 +88,7 @@ module.exports = {
             externalRequest,
             getSiteUrl: () => urlUtils.urlFor('home', true),
             getPostUrl: post => getPostUrl(post),
-            isEnabled: () => labs.isSet('webmentions') && !settingsCache.get('is_private')
+            isEnabled: () => !settingsCache.get('is_private')
         });
         sendingService.listen(events);
     }

ghost/core/test/e2e-server/services/mentions.test.js

@@ -31,8 +31,6 @@ describe('Mentions Service', function () {
     });
 
     beforeEach(async function () {
-        await mockManager.mockLabsEnabled('webmentions');
-
         // externalRequest does dns lookup; stub to make sure we don't fail with fake domain names
         sinon.stub(dnsPromises, 'lookup').callsFake(function () {
             return Promise.resolve({address: '123.123.123.123'});
@@ -72,18 +70,6 @@ describe('Mentions Service', function () {
                 assert.equal(endpointMock.isDone(), false);
             });
 
-            it('Respects the disabled flag', async function () {
-                await mockManager.mockLabsDisabled('webmentions');
-                let publishedPost = {status: 'published', ...mentionsPost};
-                await agent
-                    .post('posts/')
-                    .body({posts: [publishedPost]})
-                    .expectStatus(201);
-
-                assert.equal(mentionMock.isDone(), false);
-                assert.equal(endpointMock.isDone(), false);
-            });
-
             it('Email only post published', async function () {
                 let publishedPost = {status: 'published', email_only: true, ...mentionsPost};
                 await agent