Show nothing instead of unassigned on issues

Created by: cirosantilli

Subjective like all UI features, but here goes:

After:

Before (shows unassigned):

I think it's natural to understand that if there is no "Assigned to" then there it is unassigned.

Otherwise it produces too much interface clutter, e.g. from GitLab CE:

When we have a single object to show, saying not there is OK. But on lists / tables where information is already overflowing, I'd rather not show anything.