Re-enable libcore test WeakHashMapTest#test_keySet.

Remove it from the list of ignored libcore test failures.

Test: art/tools/run-libcore-tests.sh --mode=host --variant=X64 (with ART built with `ART_USE_READ_BARRIER=true` and `ART_HEAP_POISONING=true`)
Bug: 25437292
Change-Id: I307f306eed315026efa66a1e026ea63c65aed40b
1 file changed