Docs/admin-guide/cgroup-v2: drop stale misc interface file count

Docs/admin-guide/cgroup-v2: drop stale misc interface file count

The Miscellaneous controller documentation states it "provides 3 interface
files", but misc_cg_files[] actually registers six (max, current, peak,
capacity, events, events.local). Drop the stale count and let the file
list that follows speak for itself.

Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
Signed-off-by: Tejun Heo <tj@kernel.org>