Removed old activitypub flag

- we have another flag with a different casing and that's the one that
  is used, so `activitypub` can be deleted

ghost/core/core/shared/labs.js

@@ -27,7 +27,6 @@ const GA_FEATURES = [
 //       input for the "labs" setting value
 const BETA_FEATURES = [
     'additionalPaymentMethods',
-    'activitypub',
     'stripeAutomaticTax',
     'webmentions',
     'editorExcerpt',

ghost/core/test/e2e-api/admin/__snapshots__/config.test.js.snap

@@ -11,7 +11,6 @@ Object {
     "labs": Object {
       "ActivityPub": true,
       "NestPlayground": true,
-      "activitypub": true,
       "additionalPaymentMethods": true,
       "adminXDemo": true,
       "announcementBar": true,

ghost/core/test/integration/importer/v2.test.js

@@ -824,7 +824,7 @@ describe('Importer', function () {
 
             exportData.data.settings[0] = testUtils.DataGenerator.forKnex.createSetting({
                 key: 'labs',
-                value: JSON.stringify({activitypub: true})
+                value: JSON.stringify({additionalPaymentMethods: true})
             });
 
             return dataImporter.doImport(exportData, importOptions)
@@ -835,7 +835,7 @@ describe('Importer', function () {
                 .then(function (result) {
                     should.equal(result.attributes.key, 'labs');
                     should.equal(result.attributes.group, 'labs');
-                    should.equal(result.attributes.value, '{"activitypub":true}');
+                    should.equal(result.attributes.value, '{"additionalPaymentMethods":true}');
                 });
         });
 

ghost/core/test/regression/api/admin/settings.test.js

@@ -79,11 +79,11 @@ describe('Settings API', function () {
         it('Can edit only allowed labs keys', async function () {
             await checkCanEdit('labs',
                 JSON.stringify({
-                    activitypub: true,
+                    additionalPaymentMethods: true,
                     gibberish: true
                 }),
                 {
-                    activitypub: true
+                    additionalPaymentMethods: true
                 }
             );
         });