Relax checks on unused imports

This is definitely worth a warning but should not make builds fail for
users. We deny warnings in CI and sort this out before integrating.

See issue #169 for more details.

.github/workflows/build.yaml

@@ -46,6 +46,8 @@ env:
   CARGO_TERM_COLOR: always
   # Enable cross compilation for `pkg_config`.
   PKG_CONFIG_ALLOW_CROSS: 1
+  # Deny warnings.
+  RUSTFLAGS: -D warnings
 
 jobs:
   build:

src/lib.rs

@@ -19,8 +19,7 @@
 #![deny(
     missing_docs,
     missing_debug_implementations,
-    missing_copy_implementations,
-    unused
+    missing_copy_implementations
 )]
 // Document feature-gated elements on docs.rs. See
 // https://doc.rust-lang.org/rustdoc/unstable-features.html?highlight=doc(cfg#doccfg-recording-what-platforms-or-features-are-required-for-code-to-be-present