Remove app icon from USB dialogs

Per material design guidelines, dialogs should not
have an icon in the dialog title. This affects both
the UsbConfirmActivity (allowing an app to handle a
specific USB device) and the UsbPermissionActivity
(allowing an app to access a specific USB device).

Test: visual inspection
BUG: 69165031
Change-Id: I8e4d6e97a450236d121020e25efd43773b4bb9c5