Use -D warnings instead of deny-warnings feature.

clippy_lints/Cargo.toml

@@ -32,7 +32,6 @@ url = "2.2"
 walkdir = "2.3"
 
 [features]
-deny-warnings = ["clippy_config/deny-warnings", "clippy_utils/deny-warnings"]
 # build clippy with internal lints enabled, off by default
 internal = ["serde_json", "tempfile", "regex"]
 

clippy_lints/src/lib.rs

@@ -14,7 +14,6 @@
 #![feature(stmt_expr_attributes)]
 #![feature(unwrap_infallible)]
 #![recursion_limit = "512"]
-#![cfg_attr(feature = "deny-warnings", deny(warnings))]
 #![allow(
     clippy::missing_docs_in_private_items,
     clippy::must_use_candidate,