Relax any sequence schema restrictions

[ghost]

The potential use of Fn::If can muck with even the most basic restriction to have a sequence. The Fn::If is a Hash, but could have a legit array "output".

This could play in with #10 but in the meantime, probably makes sense to reduce the schema validators to only include required fields and set them to any. For each field we make this change, we need to check there isn't a core rule that will be affected in an undesirable way (i.e. something it needs to check itself that previously it depended upon being correct).