refactor: remove #![feature(const_ptr_offset)]

The `const_ptr_offset` feature was stabilized by
<rust-lang/rust#93957>.

Author: yvt

src/r3_core/src/lib.rs

@@ -25,7 +25,6 @@
 #![feature(const_result_drop)]
 #![feature(const_slice_index)]
 #![feature(const_option_ext)]
-#![feature(const_ptr_offset)]
 #![feature(const_trait_impl)]
 #![feature(const_ptr_write)]
 #![feature(core_intrinsics)]

src/r3_kernel/src/lib.rs

@@ -11,7 +11,6 @@
 #![feature(maybe_uninit_slice)]
 #![feature(const_slice_index)]
 #![feature(const_option_ext)]
-#![feature(const_ptr_offset)]
 #![feature(const_trait_impl)]
 #![feature(const_ptr_write)]
 #![feature(core_intrinsics)]

src/r3_port_arm/src/lib.rs

@@ -1,6 +1,5 @@
 #![feature(const_ptr_offset_from)]
 #![feature(const_refs_to_cell)]
-#![feature(const_ptr_offset)]
 #![feature(const_trait_impl)]
 #![feature(naked_functions)]
 #![feature(const_mut_refs)]

src/r3_port_riscv_test_driver/src/main.rs

@@ -1,6 +1,5 @@
 #![feature(const_refs_to_cell)]
 #![feature(const_trait_impl)]
-#![feature(const_ptr_offset)]
 #![feature(naked_functions)]
 #![feature(const_mut_refs)]
 #![feature(decl_macro)]