Bug: 18542685.
This CL includes two changes:
* Fixed a leak of DeathRecipient when geofences are removed from the
hardware.
* Avoid creating more DeathRecipient than needed. Use the underlying
binder object instead of the callback object to tell if they are the
same. So if the client passes the same callback instance to
GeofenceHardwareImpl, only one DeathRecipient is created.
Change-Id: I7809e4bc04df4f9e3590de98a03178b276c821ea
4cc80a758c