Revert "Fixes #655 - Ensure that isActivie on Skus also takes into account the ‘available’ flag. Also, if the available flag is not explicitly set on a Sku then the Sku should still be marked as available."

This reverts commit 0dc7efc5fe80e546dca56397b7dcd1635de0f016.
#655 - Provide better docs for Sku availability and default the availability to ‘true’ rather than null