Revert "Re-enable libcore test WeakHashMapTest#test_keySet."

This reverts commit d3a36fd9d99857da60777ddcf3b10058402e0915.

Reverting as the test still fails on the ART Buildbot.

Bug: 25437292
Change-Id: Id8bf59bac2d81554d5a50757ce25255ec99155ec
1 file changed