core/cgroup: drop extraneous CGRuntime check in unit_get_memory_available()

Currently, for units whose CGRuntime is not allocated just yet, e.g.
inactive ones, MemoryAvailable fails to account for their MemoryMax/High
settings. Let's remove the CGRuntime check hence. The call to
unit_get_memory_accounting() would certainly fail, but it doesn't matter,
since 'current' is initially set to 0 anyways.

src/core/cgroup.c

@@ -4501,10 +4501,6 @@ int unit_get_memory_available(Unit *u, uint64_t *ret) {
                 if (!unit_context)
                         return -ENODATA;
 
-                CGroupRuntime *crt = unit_get_cgroup_runtime(u);
-                if (!crt || !crt->cgroup_path)
-                        continue;
-
                 (void) unit_get_memory_accounting(u, CGROUP_MEMORY_CURRENT, &current);
                 /* in case of error, previous current propagates as lower bound */