Fix memory leak in TCMS when TCSession.destroy() is not called.

TCMS stores sessions in a Map and remove it when the session is
destroyed. Memory leak happens if the client forget to call
TCSession.destroy() or does not have a chance to call before the process
is dead.

Solution:
1. Use linkToDeath() to remove the cached session when client process
   is dead. TCSessionID now contains a binder to make this possible.
2. Install a Cleaner to TCSession object such that destroy() is called
   whenever the session object is going to be GCed. This is needed
   because some clients may have a long lifecycle, e.g. apps that are
   bounded by system.

BUG:149012454

Test: Write an app that creates a TC session, but not calling destory().
      Then make sure TCMS removed the session in the following situations:
      1. The app is killed
      2. TCSession object is GCed (By forcing GC)
      By checking the output dumpsys textclassificataion, we can know
      that the session object is removed
Test: mts-tradefed run mts-extservices
Test: Sanity test: smart selection + smart replies

Change-Id: Ifb7dcb23e1f50d4b3e97a6ce40e63b57193f2892