qapi: fix example of query-cpus-fast command

Example output contains member @arch that was removed in 445a5b4087
"machine: remove 'arch' field from 'query-cpus-fast' QMP command". Fix
it.

Signed-off-by: Victor Toso <victortoso@redhat.com>
Message-Id: <20220331190633.121077-9-victortoso@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

qapi/machine.json

@@ -109,7 +109,6 @@
 #                 "socket-id": 0
 #             },
 #             "qom-path": "/machine/unattached/device[0]",
-#             "arch":"x86",
 #             "target":"x86_64",
 #             "cpu-index": 0
 #         },
@@ -121,7 +120,6 @@
 #                 "socket-id": 1
 #             },
 #             "qom-path": "/machine/unattached/device[2]",
-#             "arch":"x86",
 #             "target":"x86_64",
 #             "cpu-index": 1
 #         }