Allow DO to provision even if it has set disallow remove mp.

If the device owner has set DISALLOW_REMOVE_MANAGED_PROFILE,
and there is already a managed profile:
it should be allowed to provision a new managed profile by
deleting the old one.
Test: adb shell am instrument -e class
com.android.server.devicepolicy.DevicePolicyManagerTest
-w
com.android.frameworks.servicestests/android.support.test.runner.AndroidJUnitRunner
BUG:34116228

Change-Id: I9e6f39924107aee40b57d22e638487a1ea3132de
diff --git a/services/core/java/com/android/server/pm/UserManagerService.java b/services/core/java/com/android/server/pm/UserManagerService.java
index 1eb8b94..7c81cf1 100644
--- a/services/core/java/com/android/server/pm/UserManagerService.java
+++ b/services/core/java/com/android/server/pm/UserManagerService.java
@@ -2347,6 +2347,12 @@
     }
 
     @Override
+    public boolean removeUserEvenWhenDisallowed(@UserIdInt int userHandle) {
+        checkManageOrCreateUsersPermission("Only the system can remove users");
+        return removeUserUnchecked(userHandle);
+    }
+
+    @Override
     public UserInfo createUser(String name, int flags) {
         checkManageOrCreateUsersPermission(flags);
         return createUserInternal(name, flags, UserHandle.USER_NULL);