integration/container: TestKillDifferentUserContainer: adjust API version
TestKillDifferentUserContainer was migrated from integration-cli in
commit 0855922cd3cd1e9d846fd85ef968653ff8649a44. Before migration, it
was not using a specific API version, so we can assume "current"
API version.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>