kset: remove decl_subsys macro

This macro is no longer used.  ksets should be created dynamically with
a call to kset_create_and_add() not declared statically.

Yes, there are 5 remaining static struct kset usages in the kernel tree,
but they will be fixed up soon.

Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>