Revert "Fix double variable interpolation in branch name"
Revert "Fix double variable interpolation in branch name"

This reverts commit 6cbd49ad5c4cfa1d2e1dc5daf4a1e45c8596097a because it
broke users prompts if they didn't have `prompt_subst` set.

depressiveRobot/pure-time,joshuarubin/dotfiles,forivall/pure,sindresorhus/pure,joshuarubin/dotfiles,mafredri/pure,joshuarubin/dotfiles,DFurnes/purer,jaredru/zsh-pure,dmiedema/pure,supercrabtree/pure,kgrz/pure,joshuarubin/dotfiles