revert: restore #![allow(dead_code)] - CI clippy -D warnings conflict (#3979)

revert: restore #![allow(dead_code)] - clippy -D warnings treats warn as error

The #742 PR changed #![allow(dead_code)] to #![warn(dead_code)], but
CI runs clippy with -D warnings which turns warnings into errors.
This caused CI failures across multiple PRs.

Reverting to #![allow(dead_code)] until the dead code is actually
cleaned up. The 189 warnings in ecstore should be fixed incrementally
by deleting dead code and adding item-level allows, not by changing
the crate-level policy.

crates/ecstore/src/lib.rs

@@ -1,4 +1,4 @@
-#![warn(dead_code)] // Gradually clean up dead code; see https://github.com/rustfs/backlog/issues/742
+#![allow(dead_code)]
 // Copyright 2024 RustFS Team
 //
 // Licensed under the Apache License, Version 2.0 (the "License");