Do not show the redundant RemoveAccountFailureDialog

When the AccountManager's confirm remove dialog is canceled, a redundant
ConfirmRemoveAccountDialog showed up.

- Only show the dialog when a real error reported from AccountManager
- Also change RemoveAccountFailureDialog's title to remove the redundant
  question mark

Fix: 204948166
Test: manual
Change-Id: If712e120938e80e1bf4593fa78a1a2a70684fc2a