zshrc: asc?

[zeha]

As noted in #229 maybe asc has become obsolete.

@ft @mika wdyt?

[mika]

I do not use asc either, it also hardcodes screen usage, while I assume folks use tmux nowadays more often, and also mosh exists. So fine by me to drop it, if anyone needs that it certainly could go into people's custom zshrc. :)