message: enable keras backend_test testBigRollup, formerly skipped for slowness
diff: @@ -1734,7 +1734,6 @@ class TestBackendOps(unittest.TestCase):
  # Big rollup
  @opTest([[m(1000, 1000)]], do_grads=False)
  - @unittest.skip('This is slow (TODO: re-enable)')
  def testBigRollup(self, b, x):
  return [b.sum(x, axis=1)]
  