cgroup: remove unused variables in cgroup_destroy_locked()

{

	struct dentry *d = cgrp->dentry;

	struct cgroup *parent = cgrp->parent;

	DEFINE_WAIT(wait);

	struct cgroup_event *event, *tmp;

	struct cgroup_subsys *ss;

	LIST_HEAD(tmp_list);

	lockdep_assert_held(&d->d_inode->i_mutex);

	lockdep_assert_held(&cgroup_mutex);