qga/qapi-schema: Drop obsolete note on "unsupported" errors

The note talks about "unsupported" errors and QERR_UNSUPPORTED.  The
former is vague, and the latter makes sense only in C, not in external
interface documentation.  Fortunately, we don't have to address this
anymore: recent merge commit 3b5efc553eb got rid of these errors.
Delete the note.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240911131206.2503035-2-armbru@redhat.com>
1 file changed