fix AttributeError on Bookmark.__str__

[Bomme]

Issue(s)
fixes FREESOUND-WEB-1V5 and FREESOUND-WEB-1V4

Description

AttributeError: 'Bookmark' object has no attribute 'name'
(14 additional frame(s) were not displayed)
...
  File "bookmarks/models.py", line 43, in __str__
    return f"Bookmark: {[self.name](http://self.name/)}"

Deployment steps:

[ffont]

Oh thanks! I removed the name property some time ago :S