Refactor: scheduler: don't include originally unpacked resource parameters in digest
    
    Previously, when calculating an operation digest, calculate_main_digest() would
    grab the following, in order of highest to lowest precedence:
    
    * instance attributes evaluated for the appropriate node
    * instance attributes specified with the operation
    * instance attributes as originally unpacked (without evaluating for any node)
    * resource meta-attributes
    
    Adding the originally unpacked instance attributes was redundant, since
    node-evaluated instance attributes would always be a superset of those and
    would take precedence.