Remove sun.nio.fs.UnixChannelFactory from preloaded-classes

The tests use the preloaded classes to create the core image and
that leads to UnixChannelFactory being initialized despite the
fact that FileDescriptor is not. This manifests with a null pointer
crash in tests.

Bug: 80495283
Test: m test-art-host
Change-Id: I785104e6c69c605b16357a9557b203b489972261