DEVDOCS-6186 - Remove Beta label from Form Fields Doc (#746)

<!-- Ticket number or summary of work -->
# [DEVDOCS-6186]


## What changed?
<!-- Provide a bulleted list in the present tense -->
* Feature is now in GA
* Removing Beta messaging from doc

## Release notes draft
* Storefront Form Fields API endpoint is now GA.
* We've removed the Beta messaging from the documentation.

## Anything else?
<!-- Add related PRs, salient notes, additional ticket numbers, etc. -->

ping {names}


[DEVDOCS-6186]:
https://bigcommercecloud.atlassian.net/browse/DEVDOCS-6186?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

reference/form_fields.sf.yml

@@ -1,15 +1,13 @@
 openapi: '3.0.1'
 info:
-  title: Storefront Form Fields (Beta)
+  title: Storefront Form Fields
   description: |-
     Read form fields on BigCommerce-hosted storefronts. To work with headless storefronts, use the [GraphQL Storefront API](/graphql-storefront/reference).
     
     The REST Storefront API uses [CORS](https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS) headers for authentication, and therefore has no required scopes. You do not need to send any BigCommerce-specific tokens with your requests to these endpoints.
         
     For info about authenticating BigCommerce APIs, see [Authentication and Example Requests](/docs/start/authentication#same-origin-cors-authentication).
 
-    > #### Warning
-    > Breaking changes may be introduced to this endpoint while in beta.
   version: ''
   termsOfService: 'https://www.bigcommerce.com/terms'
   contact: