Fix reference loop in IEventQueue implementation.

EventQueue's destructor is never called because
EventQueueLooperCallback has a strong reference to it,
and EventQueueLooperCallback is never destroyed because
the file descriptor is never removed from the looper.

Bug: 37280081
Test: camera works
Test: event queue is destroyed when client removes
its reference (from logcat)

Change-Id: I12347b6d1cca354288382555d2d9a20acfa59233