cgroup: drop "ignore_self" argument from cg_is_empty()

In all cases where the function (or cg_is_empty_recursive()) ignoring
the calling process is actually wrong, as a process keeps a cgroup busy
regardless if its the current one or another. Hence, let's simplify
things and drop the "ignore_self" parameter.

src/shared/cgroup-show.c

@@ -152,7 +152,7 @@ int show_cgroup_by_path(const char *path, const char *prefix, unsigned n_columns
                 if (!k)
                         return -ENOMEM;
 
-                if (!(flags & OUTPUT_SHOW_ALL) && cg_is_empty_recursive(NULL, k, false) > 0)
+                if (!(flags & OUTPUT_SHOW_ALL) && cg_is_empty_recursive(NULL, k) > 0)
                         continue;
 
                 if (!shown_pids) {