kobject documentation: remove default_attrs information

kobject documentation: remove default_attrs information

Since commit aa30f47cf666 ("kobject: Add support for default attribute
groups to kobj_type") we have been encouraging the use of default_groups
instead of default_attrs, so reflect that information in the
documentation as well so that no new users get added while the kernel is
converted over to not use this field anymore.

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20220104105024.1014313-1-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>