warning: refname 'HEAD' is ambiguous
The problem is that you have a branch called HEAD which is absolutely dangerous, since that's the symbolic name for whatever branch is the current branch.
Rename it:
git branch -m HEAD newbranch
then you can examine it and decide what to do (delete it, or save under a descriptive branch name)
(The origin/HEAD remote branch is not a problem)
Also, this will delete the branch, if you just don't want it.
git branch -d HEAD
Use a capital -D to force the deletion:
git branch -D HEAD