Removes nested list argument.

[maraca]

auto_rollback_events, lb_listener_arns, and test_traffic_route_listener_arns are already declared as lists in the variables.tf. By passing those arguments inside of a list terraform is throwing errors since it expect to read a single element from the list, not a nested list.

See https://github.com/tmknom/terraform-aws-codedeploy-for-ecs/blob/master/variables.tf#L17