Remove unused extern crate declarations

These declarations are not needed.
This avoids the #[deny(unused_extern_crates)] lint, implied by #[deny(rust_2018_idioms)]

This error only occurs when the `nested-values` feature is enabled.
This error also seems to only occur on new versions (ex. 1.72 is fine).

Switch #[deny(rust_2018_idioms)] to #[warn(...)] to avoid unnecessary
build failures in the future.

CHANGELOG.md

@@ -8,6 +8,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 * Fix some internal warnings
   * Example: Avoid the new [`#[warn(unexpected_cfgs)]`](https://blog.rust-lang.org/2024/05/06/check-cfg.html) lint.
   * None of these should affect user crates
+* nested-values: Fix CI failure caused by `#[deny(unused_extern_crates)]` lint
+  * Switch `#[deny(rust_2018_idioms)]` to `#[warn(...)]` to avoid unnecessary build failures in the future.
+  * I don't *think* this should affect user code.
 
 ### 2.8.0-beta.2 - 2024-01-05
 

src/lib.rs

@@ -278,7 +278,7 @@
 
 // {{{ Imports & meta
 #![warn(missing_docs)]
-#![deny(rust_2018_idioms)]
+#![warn(rust_2018_idioms)]
 #![no_std]
 
 #[cfg(not(feature = "std"))]
@@ -300,11 +300,6 @@ use alloc::string::String;
 #[cfg(not(feature = "std"))]
 use alloc::{sync::Arc, vec::Vec};
 
-#[cfg(feature = "nested-values")]
-extern crate erased_serde;
-#[cfg(feature = "nested-values")]
-extern crate serde;
-
 use core::str::FromStr;
 use core::{convert, fmt, result};
 #[cfg(feature = "std")]