docs/devel/qapi-code-gen: Don't reserve types ending with 'Kind'

We reserved type names ending with 'Kind' because a simple union
'SomeSimpleUnion' generated both a struct type SomeSimpleUnion and an
enum type SomeSimpleUnionKind.  Gone since commit 4e99f4b12c0 (qapi:
Drop simple unions).  The commit neglected to update the documentation
not to reserve type names ending with 'Kind'.  Do that now.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20231221145727.835905-1-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

docs/devel/qapi-code-gen.rst

@@ -737,9 +737,8 @@ Types, commands, and events share a common namespace.  Therefore,
 generally speaking, type definitions should always use CamelCase for
 user-defined type names, while built-in types are lowercase.
 
-Type names ending with ``Kind`` or ``List`` are reserved for the
-generator, which uses them for implicit union enums and array types,
-respectively.
+Type names ending with ``List`` are reserved for the generator, which
+uses them for array types.
 
 Command names, member names within a type, and feature names should be
 all lower case with words separated by a hyphen.  However, some