Remove macro_use

As of Rust 2018, macro_use is no longer required in most circumstances.
I think it is generally a good idea to remove these when not needed, to
stop them from polluting the crate's global namespace.
https://doc.rust-lang.org/edition-guide/rust-2018/macros/macro-changes.html#macro_rules-style-macros

nix-rust/src/lib.rs

@@ -1,14 +1,3 @@
-#[macro_use]
-extern crate lazy_static;
-
-#[cfg(test)]
-#[macro_use]
-extern crate assert_matches;
-
-#[cfg(test)]
-#[macro_use]
-extern crate proptest;
-
 #[cfg(not(test))]
 mod c;
 mod error;