Localize "Driver" string and some API cleanup

Moved "Driver" string to an overlay so it can get localized.

Added an API to create an admin with a default user name.

Deleted the .mk file as it wasn't being used to compile anything
anymore.

I also cleaned up some javadoc for the removeUser(), added some missing
tests for removeUser() around last admin functionality, and added some
new tests for the new APIs.

Test: Ran 'atest CarServiceUnitTest'. Existing and new tests pass.

BUG:111438127
BUG:115656969
Change-Id: I6e186242415902434f380d35c6fdf09a3950ea0a
(cherry picked from commit 4947c4a831a7b92dbd98ce375b1dda25da27142f)
5 files changed