encoding/jsonschema: remove draft-05 version

The draft-05 JSON Schema version does not exist,
and should not be used [1].

[1] https://json-schema.org/draft-06/json-schema-release-notes#q:-what-happened-to-draft-05

Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: Ie00e9d7619fbcdb15c89e65412b47b39ef9ec949
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1199485
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>

encoding/jsonschema/version.go

@@ -11,11 +11,11 @@ type schemaVersion int
 const (
 	versionUnknown schemaVersion = iota // unknown
 	versionDraft04                      // http://json-schema.org/draft-04/schema#
-	versionDraft05                      //	http://json-schema.org/draft-05/schema#
-	versionDraft06                      //	http://json-schema.org/draft-06/schema#
-	versionDraft07                      //	http://json-schema.org/draft-07/schema#
-	version2019_09                      // https://json-schema.org/draft/2019-09/schema
-	version2020_12                      // https://json-schema.org/draft/2020-12/schema
+	// Note: draft 05 never existed and should not be used.
+	versionDraft06 // http://json-schema.org/draft-06/schema#
+	versionDraft07 // http://json-schema.org/draft-07/schema#
+	version2019_09 // https://json-schema.org/draft/2019-09/schema
+	version2020_12 // https://json-schema.org/draft/2020-12/schema
 
 	numVersions // unknown
 )