In the case where copy fails, remove will probably succeed.
For example, if the file system were full. So we're trying
to be more careful with .zshrc here.
The messages are not accurate to what the script is doing
with .zshrc -- It says, "Backing up to .zshrc.pre-oh-my-zsh"
but the next line removes it. So we should rename .zshrc
instead of removing it before we restore the original.