refactor: remove #![feature(const_intrinsic_copy)]

The `const_intrinsic_copy` feature was stabilized by
[rust-lang/rust#97276][1].

[1]: rust-lang/rust#97276

Author: yvt

src/r3_core/src/lib.rs

@@ -19,7 +19,6 @@
 #![feature(const_cell_into_inner)]
 #![feature(const_ptr_offset_from)]
 #![feature(type_alias_impl_trait)]
-#![feature(const_intrinsic_copy)]
 #![feature(const_slice_ptr_len)]
 #![feature(exhaustive_patterns)] // `let Ok(()) = Ok::<(), !>(())`
 #![feature(generic_const_exprs)]

src/r3_kernel/src/lib.rs

@@ -7,7 +7,6 @@
 #![feature(const_precise_live_drops)]
 #![feature(const_raw_ptr_comparison)]
 #![feature(cfg_target_has_atomic)] // `#[cfg(target_has_atomic_load_store)]`
-#![feature(const_intrinsic_copy)]
 #![feature(exhaustive_patterns)] // `let Ok(()) = Ok::<(), !>(())`
 #![feature(generic_const_exprs)]
 #![feature(const_refs_to_cell)]