Remove Contract on customUserData

A common paradigm with userdata is to supply:
  userdata:
    str_replace:
      template: |
        <some script>
    params:
      param1: value1

With the contract on customUserData being a string, passing str_replace
as the argument results in coercion to a string, which makes it invalid.

Change-Id: I8bcf788522fc2428eaa3c8529ee11b5ed385099b
Merge "Remove Contract on customUserData"