Look for AsynchronousCloseMonitor in libandroidio by default.

AsynchronousCloseMonitor is moved into libandroidio by
r.android.com/910073 and so the system copy of Conscrypt no
longer needs to dlopen libjavacore. Unbundled Conscrypt
needs to continue to do so for compatability with devices
running older releases.

Bug: 123744297
Test: m && flashall
Test: atest CtsLibcoreOkHttpTestCases
Test: atest CtsLibcoreTestCases
Change-Id: Ib1bd6c0919cda16b38c87322688379188a77467b