Remove the unused success_url and return

Since 'Change Password' form handle successfully return
httpResponseRedirect(settings.LOGOUT_URL), it's no need
to set success_url and never reach the 'return True' at
the end.

Change-Id: I47c8888b07d06044fec8f06042d4ef6401e77097
Closes-Bug: #1331329
Merge "Remove the unused success_url and return"