Fix versions: None
In JIRA you can't clear the resolution without using a post-function.
Lots of customers are screaming for it - https://community.atlassian.com/t5/JIRA-questions/How-do-I-set-the-resolution-of-an-issue-to-quot-Unresolved-quot/qaq-p/143259
And there are some workarounds - https://confluence.atlassian.com/jirakb/howto-bulk-clear-resolution-635896313.html
We should either add an action or make sure edit can do it.