implemented removal of user

Signed-off-by: Stephan Richter <s.richter@srsoftware.de>

de.srsoftware.oidc.datastore.file/src/main/java/de/srsoftware/oidc/datastore/file/FileStore.java

@@ -76,7 +76,9 @@ public class FileStore implements AuthorizationService, ClientService, SessionSe
 
 	@Override
 	public UserService delete(User user) {
-		return null;
+		var users = json.getJSONObject(USERS);
+		users.remove(user.uuid());
+		return save();
 	}
 
 	@Override