tomoyo: remove tomoyo_gc_thread()->daemonize()

daemonize() is only needed when a user-space task does kernel_thread().

tomoyo_gc_thread() is kthread_create()'ed and thus it doesn't need
the soon-to-be-deprecated daemonize().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: James Morris <jmorris@namei.org>