When duplicating a map, the references are also duplicated

[snipercup]

When a map is duplicated from a contentlist, the references that map has are also duplicated.

Steps to reproduce the issue:

• Open the content editor
• Select urbanroad
• Press the D button to duplicate and give it a name
• Open the newly created map json file and observe it has references even though it has just been created.

Expected behavior: When a map is duplicated, it will be brand new and should not have any references.