Trim external deps

[bbatsov]

The package uses a few external deps that are not really needed on modern Emacs:

• s.el is easily replaced with built-in functions
• dash is easily replaced with the built-in seq
• f.el can also be replaced easily with built-in functions

When it comes to external deps, less is always more. :-)

[bbatsov]

I've dropped s.el and dash.el, and there's only f-join left from f.el. Probably it'd be best to just inline it, as it's a pretty simple function, but we can do this down the road.

[zerolfx]

I saw both (require 'subr-x.el) and (require 'subr-x) in code. Are they both correct?

[bbatsov]

@zerolfx Seems I've made a silly typo. Just fixed it.

[viktorbezdek]

@bbatsov I guess the love for well written code never fades 🤘🏻

Hope you're doing great.

🫡