We don't need to wait for task in-activity in release_task() any more,

We don't need to wait for task in-activity in release_task() any more,
since we now properly reference-count the allocations and thus can't
be freeing the thread structures from underneath the task running on
another CPU.

Move "free_uid(p->user)" and "security_task_free()" to __put_task_struct(),
so that we're guaranteed to always have a user structure pointer.