cgroup: remove cgroup_attach_task_current_cg()

It's just a wrapper of cgroup_attach_task_all(), and it's no longer
used after commit 87d6a41
(vhost: fix attach to cgroups regression)

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

include/linux/cgroup.h

@@ -602,11 +602,6 @@ int cgroup_scan_tasks(struct cgroup_scanner *scan);
 int cgroup_attach_task(struct cgroup *, struct task_struct *);
 int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
 
-static inline int cgroup_attach_task_current_cg(struct task_struct *tsk)
-{
-	return cgroup_attach_task_all(current, tsk);
-}
-
 /*
  * CSS ID is ID for cgroup_subsys_state structs under subsys. This only works
  * if cgroup_subsys.use_id == true. It can be used for looking up and scanning.
@@ -669,10 +664,6 @@ static inline int cgroup_attach_task_all(struct task_struct *from,
 {
 	return 0;
 }
-static inline int cgroup_attach_task_current_cg(struct task_struct *t)
-{
-	return 0;
-}
 
 #endif /* !CONFIG_CGROUPS */