tests/integration/update.bats: rm obsoleted comment

This comment was added by commit 6cd425be2b (Allow update rt_period_us
and rt_runtime_us, Nov 4 2016), and the test case was added by commit
51baedf3f3 (Add integration for update rt period and runtime,
Nov 28 2016), making the comment obsolete.

Remove it.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

tests/integration/update.bats

@@ -38,7 +38,6 @@ EOF
     sed -i "s/\(\"resources\": {\)/\1\n${DATA}/" ${BUSYBOX_BUNDLE}/config.json
 }
 
-# TODO: test rt cgroup updating
 @test "update" {
     # XXX: Also, this test should be split into separate sections so that we
     #      can skip kmem without skipping update tests overall.