#git remote

If you just cloned a git repository with a number of remote tracking branches, and then you change your remote to a new one - say to have a fresh start - then you may want to remove all now obsolete remote branches:

git fetch -p

does the trick.

-p --prune. After fetching remove any remote tracking branches which no longer exist on the remote.

Forgot how the hack did you get remote tracking branches in the first place. Most probably you did something like this:

Delete a local git branch:

git branch -D mybranch

Delete a remote git branch: