Delete the ref based on the 'close' checkbox when a user merges locally

This is a follow up bug report from the outcome of the discussion in issue BCLOUD-13311

here is our workflow...

1. git clone git@bitbucket.org:yooture/dummy.git (done by dev on local env)
2. cd dummy (done by dev on local env)
3. git checkout -b feature/FF (done by dev on local env)
4. echo "Dany" >> contributors.txt (done by dev on local env)
5. git commit -am "dany" (done by dev on local env)
6. git push origin feature/FF (done by dev on local env)
7. create PR for "feature/FF" via Bitbucket WebUI (check "Close feature/FF after the pull request is merged") (done by dev in browser)
8. git checkout master (done by dev on local env)
9. git merge feature/FF (done by dev on local env)
10. git push origin master (done by dev on local env)
11. git fetch origin --prune (done by dev on local env)
12. git branch -r (done by dev on local env)

--> origin/feature/FF still exists

also if I do a fresh clone and list all the existing branches, feature/FF is still available...

all this is done on the origin organisation in Bitbucket (no fork is involved)

So from what was discussed with @kelwert in BCLOUD-13311, I would expect the repo "feature/FF" to be deleted after I pushed my merge commit - this seems clearly a bug on Bitbucket site then.