qapi: Fix to reject optional members with reserved names

qapi: Fix to reject optional members with reserved names

check_type() fails to reject optional members with reserved names,
because it neglects to strip off the leading '*'.  Fix that.

The stripping in check_name_str() is now useless.  Drop.

Also drop the "no leading '*'" assertion, because valid_name.match()
ensures it can't fail.

Fixes: 9fb081e0b98409556d023c7193eeb68947cd1211
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20210323094025.3569441-8-armbru@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>