Avoid hardcoding SYSTEM_USER to support HSUM

In case of headless system user mode, first human user would not be
SYSTEM_USER(user 0), so avoid harcoding for SYSTEM_USER.

Bug: 265281464
Test: atest android.devicepolicy.cts.ManagedSubscriptionsPolicyTest
Change-Id: I261867048a2a5b44d19ba5b34537b8d5201e4534

services/devicepolicy/java/com/android/server/devicepolicy/DevicePolicyManagerService.java

@@ -22741,9 +22741,10 @@ public class DevicePolicyManagerService extends IDevicePolicyManager.Stub {
                 "This policy can only be set by a profile owner on an organization-owned "
                         + "device.");
 
+        int parentUserId = getProfileParentId(caller.getUserId());
         synchronized (getLockObject()) {
             final ActiveAdmin admin = getProfileOwnerLocked(caller.getUserId());
-            if (hasUserSetupCompleted(UserHandle.USER_SYSTEM) && !isAdminTestOnlyLocked(
+            if (hasUserSetupCompleted(parentUserId) && !isAdminTestOnlyLocked(
                     admin.info.getComponent(), caller.getUserId())) {
                 throw new IllegalStateException("Not allowed to apply this policy after setup");
             }
@@ -22765,7 +22766,6 @@ public class DevicePolicyManagerService extends IDevicePolicyManager.Stub {
         if (policyType == ManagedSubscriptionsPolicy.TYPE_ALL_MANAGED_SUBSCRIPTIONS) {
             final long id = mInjector.binderClearCallingIdentity();
             try {
-                int parentUserId = getProfileParentId(caller.getUserId());
                 installOemDefaultDialerAndSmsApp(caller.getUserId());
                 updateTelephonyCrossProfileIntentFilters(parentUserId, caller.getUserId(), true);
             } finally {