CI: Add NetBSD target (#180)

* Remove the `sys-info` crate

It offers much more features than we currently use.

Additionally, it was preventing me to cross-compile for NetBSD.

Since we were just using the `hostname()` function from the crate,
I went ahead and stole it.

* Add NetBSD target

* Fix FreeBSD clippy warnings

src/steps/os/freebsd.rs

@@ -1,6 +1,4 @@
 use crate::command::CommandExt;
-use crate::config::Step;
-use crate::execution_context::ExecutionContext;
 use crate::executor::RunType;
 use crate::terminal::print_separator;
 use crate::utils::require_option;