Delete hyper-schema after move to own repo

These files (with their revision history at both
this location and their pre-archive locations)
now live in json-schema-org/json-hyperschema-spec

It seems better to just delete these than to prune
the whole history as Hyper-Schema was released from
this repo in the past.

Also update README which didn't quite reflect reality
anyway.

Author: handrews

README.md

@@ -31,9 +31,6 @@ Labels are assigned based on [Sensible Github Labels](https://github.com/Releque
     * relative-json-pointer.xml - source for the Relative JSON Pointer I-D
 * _meta-schemas and recommended output formats_
     * schema.json - JSON Schema "core" and Validation meta-schema
-    * hyper-schema.json - JSON Hyper-Schema meta-schema
-    * links.json - JSON Hyper-Schema's Link Description Object meta-schema
-    * hyper-schema-output.json - The recommended output format for JSON Hyper-Schema links
 
 The Makefile will create the necessary Python venv for you as part of the regular make target.