cgroup: Cleanup function usage

Some masks shouldn't be needed externally, so keep their functions in
the module (others would fit there too but they're used in tests) to
think twice if something would depend on them.

Drop unused function cg_attach_many_everywhere.

Use cgroup_realized instead of cgroup_path when we actually ask for
realized.

This should not cause any functional changes.

src/shared/cgroup-setup.c

@@ -655,23 +655,6 @@ int cg_attach_everywhere(CGroupMask supported, const char *path, pid_t pid, cg_m
         return 0;
 }
 
-int cg_attach_many_everywhere(CGroupMask supported, const char *path, Set* pids, cg_migrate_callback_t path_callback, void *userdata) {
-        Iterator i;
-        void *pidp;
-        int r = 0;
-
-        SET_FOREACH(pidp, pids, i) {
-                pid_t pid = PTR_TO_PID(pidp);
-                int q;
-
-                q = cg_attach_everywhere(supported, path, pid, path_callback, userdata);
-                if (q < 0 && r >= 0)
-                        r = q;
-        }
-
-        return r;
-}
-
 int cg_migrate_v1_controllers(CGroupMask supported, CGroupMask mask, const char *from, cg_migrate_callback_t to_callback, void *userdata) {
         CGroupController c;
         CGroupMask done;