qapi: Drop redundant returns-int test

qapi: Drop redundant returns-int test

qapi-schema-test was already testing that we could have a
command returning int, but burned a command name in the whitelist.
Merge the redundant positive test returns-int, and pick a name
that reduces the whitelist size.

Signed-off-by: Eric Blake <[email protected]>
Message-Id: <1444710158[email protected]>
Signed-off-by: Markus Armbruster <[email protected]>