Fix death recipient leakage of WindowTokenClient

When WindowContext#finalize is called on client side, it
will call WindowTokenClient#detachFromWindowContainerIfNeeded
to notify system server to remove the listener.
But unregisterWindowContainerListener didn't unlink its death
recipient, that causes the objects are never actual released
both on client and server side.

Bug: 233784911
Test: atest WindowContextListenerControllerTests# \
            testRegisterWindowContextListener
Change-Id: I0e203d07e485c4577f669f512123757fd2dea058