chore: remove unused features

kernel/src/main.rs

@@ -5,13 +5,9 @@
 #![feature(asm_const)]
 #![feature(cell_update)]
 #![feature(concat_idents)]
-#![feature(const_mut_refs)]
-#![feature(extern_types)]
-#![feature(fn_align)]
 #![feature(let_chains)]
 #![feature(naked_functions)]
 #![feature(panic_info_message)]
-#![feature(stmt_expr_attributes)]
 #![feature(thread_local)]
 // Test Infrastructure
 #![feature(custom_test_frameworks)]
@@ -19,6 +15,7 @@
 #![reexport_test_harness_main = "test_main"]
 // no noisy dead_code warnings
 #![allow(dead_code)]
+#![allow(clippy::identity_op)]
 
 #[macro_use]
 extern crate static_assertions;