Fix for contact deletion on tablet

After deleting a contact, we incorrectly still show the
detail page and don't select a default contact in the contact
list.

If a contact is deleted, the ContactLookupTask will not be
able to find a lookup URI for the contact, but we should
still handle this null URI by setting it to the list
and trying to find a default contact to select instead.

Also remove the extra assignment of mSelectedContactUri.
We actually do that assignment in onContactUriQueryFinished().
This is the same way it was done in the original code before
this section was refactored in ICS MR1:
I85c748389921bdff2639fff5f7713e00ba7f9f8c

Bug: 5599721
Change-Id: Ib9b9221779a6828948553fe25fbeff982961c5ed