samples/cgroup: rm unused MEMCG_EVENTS macro

MEMCG_EVENTS is never referenced in the code. Just remove it.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: zhang jiao <[e-mail]>
Acked-by: Shakeel Butt <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Muchun Song <[e-mail]>
Cc: Roman Gushchin <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

samples/cgroup/memcg_event_listener.c

···
 #include <sys/inotify.h>
 #include <unistd.h>
 
-#define MEMCG_EVENTS "memory.events"
-
 /* Size of buffer to use when reading inotify events */
 #define INOTIFY_BUFFER_SIZE 8192