cgroup-util: drop 'controller' argument from cg_enumerate_processes()

Nowadays it always takes SYSTEMD_CGROUP_CONTROLLER as controller.
Let's drop it.

No functional change, just refactoring.

src/core/cgroup.c

@@ -2857,7 +2857,7 @@ int unit_search_main_pid(Unit *u, PidRef *ret) {
         if (!crt || !crt->cgroup_path)
                 return -ENXIO;
 
-        r = cg_enumerate_processes(SYSTEMD_CGROUP_CONTROLLER, crt->cgroup_path, &f);
+        r = cg_enumerate_processes(crt->cgroup_path, &f);
         if (r < 0)
                 return r;
 

src/core/dbus-unit.c

@@ -1375,7 +1375,7 @@ static int append_cgroup(sd_bus_message *reply, const char *p, Set *pids) {
         assert(reply);
         assert(p);
 
-        r = cg_enumerate_processes(SYSTEMD_CGROUP_CONTROLLER, p, &f);
+        r = cg_enumerate_processes(p, &f);
         if (r == -ENOENT)
                 return 0;
         if (r < 0)