Per list review: qapi-code-gen.txt reserves suffixes Kind and
List only for type names, but the code rejects them for events and
commands, too.

It turns out we reject them earlier anyway: In check_name_upper() for
event names, and in check_name_lower() for command names.

Still, adjust the code for clarity over what precisely we are guarding
against.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20210421182032.3521476-15-jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>