Remove link to old Sourcegraph repo

Author: jdorfman

docs/api/graphql/index.mdx

@@ -8,7 +8,7 @@ The Sourcegraph GraphQL API supports the following types of queries:
 - Rich git-level metadata, including commits, branches, blame information, and file tree data
 - Repository and user metadata
 
-<Callout type="note">The API is under active development. Backwards compatibility will be maintained in most cases, and backwards-incompatible changes will be documented in the [changelog](https://sourcegraph.com/github.com/sourcegraph/sourcegraph/-/blob/CHANGELOG).</Callout>
+<Callout type="note">The API is under active development. Backwards compatibility will be maintained in most cases.</Callout>
 
 ## Quickstart