We had the user name on the lock screen primarily for multi-user
systems, so someone can easily see who's logged in. However,
there are some issues with it:

 - It's not immediately obvious why it's there
 - It won't be useful on single user systems (which we're
   optimising for)
 - It adds visual noise
 - There could potentially be privacy concerns - screen wakes up
   for some reason, reveals your name potentially to passersby

I think that we should drop the user name for now.