remove core conformance class from list

Author: philvarner

README.md

@@ -7,9 +7,8 @@
   - [Example](#example)
 
 - **OpenAPI specification:** [openapi.yaml](openapi.yaml) ([rendered version](https://api.stacspec.org/v1.0.0-rc.1/children))
-- **Conformance URIs:** 
+- **Conformance URI:** 
   - <https://api.stacspec.org/v1.0.0-rc.1/children>
-  - <https://api.stacspec.org/v1.0.0-rc.1/core>
 - **[Maturity Classification](https://github.com/radiantearth/stac-api-spec/blob/main/README.md#maturity-classification):** Proposal
 - **Dependencies**: [STAC API - Core](https://github.com/radiantearth/stac-api-spec/blob/main/core)