sphinx/qapidoc: Drop code to generate doc for simple union tag

QAPISchemaGenRSTVisitor._nodes_for_members() has a special case to
auto-generate documentation for a union tag member of implicit (enum)
type that lacks documentation.

This was useful for simple unions, where the tag member's type was
implicitly.  The only implicit enum type left today is 'QType'.  Not
worth a special case.  Drop.  No change to generated documentation.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240205074709.3613229-6-armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

docs/sphinx/qapidoc.py

@@ -168,12 +168,6 @@ def _nodes_for_members(self, doc, what, base=None, variants=None):
             # TODO drop fallbacks when undocumented members are outlawed
             if section.text:
                 defn = section.text
-            elif (variants and variants.tag_member == section.member
-                  and not section.member.type.doc_type()):
-                values = section.member.type.member_names()
-                defn = [nodes.Text('One of ')]
-                defn.extend(intersperse([nodes.literal('', v) for v in values],
-                                        nodes.Text(', ')))
             else:
                 defn = [nodes.Text('Not documented')]