Fix Category Import Errors. Unable to Import Root Categories

When importing root categories CategoryImporter.cs Throws 'missing
required property' error due to ParentCategoryId being a required
property.

To Fix I have changed ParentCategoryId IsRequiredProperty from TRUE to
FALSE.
Revert "Fix for: Unable to import root categories."

This reverts commit bffc0364e9359ec9ad2ba9867c554f3f0dd4cbd4.