qapi: block: Remove mentions of error types which were removed

Most of the various error classes were removed prior to the 1.2 release.
Remove mentions of the error classes which did not make it.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

qapi/block-core.json

@@ -1499,11 +1499,8 @@
 #                    autogenerated. (Since: 2.9)
 #
 # Returns: Nothing on success
-#          If commit or stream is already active on this device, DeviceInUse
 #          If @device does not exist, DeviceNotFound
-#          If image commit is not supported by this device, NotSupported
-#          If @base or @top is invalid, a generic error is returned
-#          If @speed is invalid, InvalidParameter
+#          Any other error returns a GenericError.
 #
 # Since: 1.3
 #