feat: remove netlify graph code (#400)

**Which problem is this pull request solving?**

Removes Netlify Graph code as it has reached its end of life

**List other issues or pull requests related to this problem**

https://github.com/netlify/pod-api-ecosystem/issues/174

**Checklist**

Please add a `x` inside each checkbox:

- [x] I have read the [contribution
guidelines](../blob/master/CONTRIBUTING.md).
- [x] The status checks are successful (continuous integration). Those
can be seen below.

Author: dwwoelfel

src/function/event.ts

@@ -25,5 +25,4 @@ export interface Event {
   multiValueQueryStringParameters: EventMultiValueQueryStringParameters | null
   body: string | null
   isBase64Encoded: boolean
-  netlifyGraphToken: string | undefined
 }

src/function/index.ts

@@ -2,13 +2,3 @@ export { Context as HandlerContext } from './context.js'
 export { Event as HandlerEvent } from './event.js'
 export { BuilderHandler, Handler, BackgroundHandler, HandlerCallback } from './handler.js'
 export { BuilderResponse, Response as HandlerResponse } from './response.js'
-export {
-  getSecrets,
-  getSecretsForBuild,
-  withSecrets,
-  getNetlifyGraphToken,
-  getNetlifyGraphTokenForBuild,
-  GraphTokenResponse,
-  HasHeaders,
-} from '../lib/graph.js'
-export { NetlifySecrets } from '../lib/secrets_helper.js'