Remove waiter as a property of waitStep

[thejcannon]

Not sure what this is, but:

steps:
    - waiter: foobarbaz

gives me `waiter` is not a valid property on the `wait` step, perhaps you meant `wait`?

---

Note the following pipelines are valid (hence not removing all instances of "waiter"):

steps:
    - "waiter"

steps:
    - type: waiter

steps:
    - waiter:
          wait: ~