Upgrade: remove leftover ref
Upgrade: remove leftover ref

The upgrade process leaves a left over ref:

```
$ git branch
..
  _upgrade_HEAD
..
```

This commit deletes that.

Signed-off-by: Rudi Grinberg <b1c1d8736f20db3fb6c1c66bb1455ed43909f0d8@rgrinberg.com>

hlissner/.emacs.d,hlissner/.emacs.d,hlissner/.emacs.d,hlissner/.emacs.d,hlissner/.emacs.d,hlissner/doom-emacs,hlissner/doom-emacs,hlissner/doom-emacs,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/doom-emacs,hlissner/doom-emacs,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/.emacs.d