Description:
Deleting a user through User Accounts, Usermenu->My Accounts->[unlock]->choose a user and delete does not work; the settings window disappears.


Additional info:
* package version(s)
* config and/or log files etc.


Steps to reproduce:
0. create a "test user" (for testing purpose)
1. click on User menu (top right)
2. choose "My Account"
3. click Unlock button
4. after authentication (root password)
5. click on "test user"
6. click '-' (minus) or Right-click and choose delete user
7. we will be prompted
'''Do you want to keep test user's files?
It is possible to keep the home directory, mail spool and
temporary files around when deleting a user account.'''

8. chose delete files
9. settings window disappears (crashes?)

10. if we choose 'keep files' on step 7/8 we get this prompt
'''Failed to delete user
Method "DeleteUser" with signature "x" on interface
"org.freedesktop.Accounts" doesn't exist'''

11. And if we relaunch user accounts settings, the test user is not deleted.
12. seeing /etc/passwd also shows "test" user and /home also has test folder.

thanks.

Expected behavior:
1. the account should get deleted as requested.