qapi: Clean up after removal of simple unions

Commit 4e99f4b (qapi: Drop simple unions) missed a bit of code
dealing with simple union branches.  Drop it.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20230316071325.492471-4-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

scripts/qapi/expr.py

@@ -518,7 +518,7 @@ def check_union(expr: QAPIExpression) -> None:
         source = "'data' member '%s'" % key
         check_keys(value, info, source, ['type'], ['if'])
         check_if(value, info, source)
-        check_type(value['type'], info, source, allow_array=not base)
+        check_type(value['type'], info, source)
 
 
 def check_alternate(expr: QAPIExpression) -> None: