kset: remove decl_subsys_name

The last user of this macro (pci hotplug core) is now switched over to
using a dynamic kset, so this macro is no longer needed at all.

Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>