Added startWithoutUi() call to Face Unlock AIDL interface.

This is being done in support of preview-less Face Unlock (b/14433919).  Nothing
is calling this function yet, but it will be called from a trustlet to tell Face
Unlock to authenticate in the background.

If this is committed before the corresponding Face Unlock change, Face Unlock
will not build because it would not be implementing this function, and it must
implement all functions in the interface in order to build.

Change-Id: I4aaea78d58cc5f1f7e13cb981fb9a217cd901496