Remove Application Widget from LockPatternUtils

The application widget option has been removed from Settings, and should
instead be handled by the application granted with the
SET_APPLICATION_WIDGET permission.

This change:
- removes the configuration value from the LockScreenSettings database; and
- removes the producers and consumers of the value.

Change-Id: Ia83e8d713d4455a9c898a8048a256afb7291af0b