qapi: Fix up references to long gone error classes

qapi: Fix up references to long gone error classes

Commit de253f14912e88f4 (qmp: switch to the new error format on the
wire) removed most error classes.  Several later commits mistakenly
mentioned them in documentation.  Replace them by the actual error
class there.

Fixes: 44e3e053af56 (qmp: add interface blockdev-snapshot-delete-internal-sync)
Fixes: f323bc9e8b3b (qmp: add interface blockdev-snapshot-internal-sync)
Fixes: ba1c048a8f9c (qapi: Introduce add-fd, remove-fd, query-fdsets)
Fixes: ed61fc10e8c8 (QAPI: add command for live block commit, 'block-commit')
Fixes: e4c8f004c55d (qapi: convert sendkey)
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20230425064223.820979-5-armbru@redhat.com>