Remove idenitfier/data wrapper, take 2

[dafeder]

fixes [GetDKAN/dkan/issues/3450]

• [ ] All tests pass
• [ ] JSON metadata stored in the database is not wrapped with with [{"data":{},"identifier":""}]
• [ ] API GET requests return the same JSON format as before (the data is wrapped with [{"data":{},"identifier":""}])

QA Steps

• [ ] Post a dataset with referenced entities (distributions, publisher, keyword, etc)
• [ ] Make sure that JSON metadata stored in the database is not wrapped with [{"data":{},"identifier":""}]
• [ ] Run GET requests to get entities of various schemas. Make sure that JSON output has not changed compared to 2.x.