completions: pull zsh-completions repository

We will start using completions from here.
completions: remove dzr completion (not used anymore)
completions: use zsh-completions for fabric
completions: use zsh-completions for pip
completions: use zsh-completions for socat
completions: use zsh-completions for virsh
completions: move _rfkill to zsh-completions
zsh-syntax-highlighting: use my own fork

The project doesn't seem to be alive enough to take bugfixes. Let's just
point to my fork.