Fix ReferenceTest#test_subclass.

The test was completely bogus. The specification explicitly states
that the GC will enqueue and clear references directly, without a
call to the corresponding methods on the Reference class. They are
provided for use from managed code only.

bug: 26115898
Change-Id: I2f2147771d2f24d35896b956ea38c33b907edfb6
1 file changed