Use phone icon for the back action in call log details.

In order for this to work, I had to also change the default icon for the
call log details activity. However, is that is logically part of the
phone app, it is reasonable to change it, even if it does not appear on
its own in the launcher.

Bug: 5105565
Change-Id: Ibe09f0ad17f5ed03b2236443cc9a3c8f192ce18f