mm/memcontrol.c: remove unused private flag of memory.oom_control

There is no use for the private value, __OOM_TYPE and OOM notifier
OOM_CONTROL.  Therefore remove them to make the code clean.

Link: https://lkml.kernel.org/r/20220421122755.40899-1-lujialin4@huawei.com
Signed-off-by: Lu Jialin <lujialin4@huawei.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memcontrol.c

@@ -209,7 +209,6 @@ static struct move_charge_struct {
 enum res_type {
 	_MEM,
 	_MEMSWAP,
-	_OOM_TYPE,
 	_KMEM,
 	_TCP,
 };
@@ -217,8 +216,6 @@ enum res_type {
 #define MEMFILE_PRIVATE(x, val)	((x) << 16 | (val))
 #define MEMFILE_TYPE(val)	((val) >> 16 & 0xffff)
 #define MEMFILE_ATTR(val)	((val) & 0xffff)
-/* Used for OOM notifier */
-#define OOM_CONTROL		(0)
 
 /*
  * Iteration constructs for visiting all cgroups (under a tree).  If
@@ -4887,7 +4884,6 @@ static struct cftype mem_cgroup_legacy_files[] = {
 		.name = "oom_control",
 		.seq_show = mem_cgroup_oom_control_read,
 		.write_u64 = mem_cgroup_oom_control_write,
-		.private = MEMFILE_PRIVATE(_OOM_TYPE, OOM_CONTROL),
 	},
 	{
 		.name = "pressure_level",