cgroup: Remove resource_counter.txt in Documentation/cgroup-legacy/00-INDEX.

Signed-off-by: Yuan Sun <sunyuan3@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Documentation/cgroup-legacy/00-INDEX

@@ -24,7 +24,5 @@ net_prio.txt
 	- Network priority cgroups details and usages.
 pids.txt
 	- Process number cgroups details and usages.
-resource_counter.txt
-	- Resource Counter API.
 unified-hierarchy.txt
 	- Description the new/next cgroup interface.