oldhepdata: remove default None values for the data_license in submission.yaml

[GraemeWatt]

Remove these lines:

hepdata-converter/hepdata_converter/parsers/__init__.py

Lines 53 to 57 in 65c338a

	'data_license': {
	'name': None,
	'url': None,
	'description': None # (optional)
	},

since None is not a valid value of these fields in version 1.0.0 of the schema, where a string is expected. This problem has been worked around in the code for the main web app (HEPData/hepdata) by temporarily validating using version 0.1.0 of the schema if uploading an oldhepdata file, where no checks at all were made on the data_license. The temporary fix to validate using version 0.1.0 of the schema should be removed after this issue is closed and a new hepdata-converter version is made available.