chore: Use the unexpected_cfgs option in the Cargo.toml file

This allows us to use the unexpected_cfgs lint even though we have the
fuzzing cfg. More info can be found here[1].

[1]: rust-lang/cargo#13913

Cargo.toml

@@ -16,6 +16,9 @@ rust-version = "1.65"
 all-features = true
 rustdoc-args = ["--cfg", "docsrs"]
 
+[lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(fuzzing)'] }
+
 [features]
 default = ["libolm-compat"]
 js = ["getrandom/js"]

src/lib.rs

@@ -206,7 +206,6 @@
     unused_qualifications,
     rust_2018_idioms
 )]
-#![allow(unexpected_cfgs)]
 #![cfg_attr(docsrs, feature(doc_auto_cfg))]
 
 mod cipher;