Remove reference to deprecated drf-openapi package (#6398)

Author: johnthagen

docs/api-guide/schemas.md

@@ -827,19 +827,11 @@ A short description of the meaning and intended usage of the input field.
 [drf-yasg][drf-yasg] generates [OpenAPI][open-api] documents suitable for code generation - nested schemas,
 named models, response bodies, enum/pattern/min/max validators, form parameters, etc.
 
-
-## DRF OpenAPI
-
-[DRF OpenAPI][drf-openapi] renders the schema generated by Django Rest Framework
-in [OpenAPI][open-api] format.
-
-
 [cite]: https://blog.heroku.com/archives/2014/1/8/json_schema_for_heroku_platform_api
 [coreapi]: https://www.coreapi.org/
 [corejson]: https://www.coreapi.org/specification/encoding/#core-json-encoding
 [drf-yasg]: https://github.com/axnsan12/drf-yasg/
 [open-api]: https://openapis.org/
-[drf-openapi]: https://github.com/limdauto/drf_openapi
 [json-hyperschema]: https://json-schema.org/latest/json-schema-hypermedia.html
 [api-blueprint]: https://apiblueprint.org/
 [static-files]: https://docs.djangoproject.com/en/stable/howto/static-files/