Follow-up to #203. In that issues we've found out that the built packages don't work correctly on some Debian versions.
We've (@mcginty I think?) when manually removed them from the 1.5.4 release artifacts, and they have been provided by 3rd party repositories since.
So drop the CI jobs.
Using nightly one leads to having to resolve lints more frequently than rust releases, which is
getting inconvenient.
It also leads to a small compatibility issue with stable clippy: if we need to #[allow] a lint that
is only present in nightly clippy, then stable clippy complains about unknown ling in the `allow`.
* Tidy code a bit thanks to clippy
Clippy 1.54 newly detects some redundant constructs, that's nice.
sort_unstable() should yield exact same results as sort() for `Vec<&str>`
and could be faster, clippy says.
* Add clippy to CI
Matěj Laitl