Cleaned up "Embeddable signup form" GA feature flag (#20577)

no issue

- "Embeddable signup form" feature was released in Ghost
[v5.51.0](https://github.com/TryGhost/Ghost/releases/tag/v5.51.0)
(commit: 5e7edb9)
- [Project
details](https://www.notion.so/ghost/Embeddable-signup-forms-1632735f1f894d01be491aeffb48bd45?pvs=4)

apps/admin-x-framework/src/test/acceptance.ts

@@ -76,7 +76,6 @@ const defaultLabFlags = {
     themeErrorsNotification: false,
     outboundLinkTagging: false,
     announcementBar: false,
-    signupForm: false,
     members: false
 };
 

apps/admin-x-settings/src/components/settings/growth/GrowthSettings.tsx

@@ -18,7 +18,6 @@ export const searchKeywords = {
 const GrowthSettings: React.FC = () => {
     const hasTipsAndDonations = useFeatureFlag('tipsAndDonations');
     const hasRecommendations = useFeatureFlag('recommendations');
-    // const hasOffersLabs = useFeatureFlag('adminXOffers');
     const {config, settings} = useGlobalData();
     const hasStripeEnabled = checkStripeEnabled(settings || [], config || {});
 

ghost/admin/app/services/feature.js

@@ -68,7 +68,6 @@ export default class FeatureService extends Service {
     @feature('i18n') i18n;
     @feature('announcementBar') announcementBar;
     @feature('signupCard') signupCard;
-    @feature('signupForm') signupForm;
     @feature('collections') collections;
     @feature('mailEvents') mailEvents;
     @feature('collectionsCard') collectionsCard;

ghost/core/core/shared/labs.js

@@ -19,7 +19,6 @@ const GA_FEATURES = [
     'themeErrorsNotification',
     'outboundLinkTagging',
     'announcementBar',
-    'signupForm',
     'recommendations',
     'newEmailAddresses',
     'internalLinking'

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

@@ -1155,7 +1155,7 @@ exports[`Settings API Edit Can edit a setting 2: [headers] 1`] = `
 Object {
   "access-control-allow-origin": "http://127.0.0.1:2369",
   "cache-control": "no-cache, private, no-store, must-revalidate, max-stale=0, post-check=0, pre-check=0",
-  "content-length": "4499",
+  "content-length": "4479",
   "content-type": "application/json; charset=utf-8",
   "content-version": StringMatching /v\\\\d\\+\\\\\\.\\\\d\\+/,
   "etag": StringMatching /\\(\\?:W\\\\/\\)\\?"\\(\\?:\\[ !#-\\\\x7E\\\\x80-\\\\xFF\\]\\*\\|\\\\r\\\\n\\[\\\\t \\]\\|\\\\\\\\\\.\\)\\*"/,