Prune abandoned autofill sessions

Regularly check if the sessions are still valid and clear the ones that
are not.

Test: 1. Started session in dialer
      2. Home button (dialer goes in background)
      3. kill -9 dialer
      4. Wait 30 seconds
      5. Start session is messenger
      6. dialer session stays

      1. Started session in dialer
      2. Home button (dialer goes in background)
      3. kill -9 dialer
      4. Swipe dialer from recents
      5. Wait 30 seconds
      5. Start session is messenger
      6. dialer session is removed
Fixes: 38005472

Change-Id: I8199ce44777b313141ee1eab6c8de5ad5089474a