refactor(core,port_arm,port_arm_m): remove #![feature(const_ptr_offset_from)]

The `const_ptr_offset_from` feature was stabilized by
[rust-lang/rust#96240][1].

[1]: rust-lang/rust#96240

Author: yvt

src/r3_core/src/lib.rs

@@ -16,7 +16,6 @@
 #![feature(const_slice_first_last)]
 #![feature(cfg_target_has_atomic)] // `#[cfg(target_has_atomic_load_store)]`
 #![feature(const_cell_into_inner)]
-#![feature(const_ptr_offset_from)]
 #![feature(type_alias_impl_trait)]
 #![feature(const_slice_ptr_len)]
 #![feature(exhaustive_patterns)] // `let Ok(()) = Ok::<(), !>(())`

src/r3_port_arm/src/lib.rs

@@ -1,4 +1,3 @@
-#![feature(const_ptr_offset_from)]
 #![feature(const_refs_to_cell)]
 #![feature(generic_arg_infer)]
 #![feature(const_trait_impl)]

src/r3_port_arm_m/src/lib.rs

@@ -1,4 +1,3 @@
-#![feature(const_ptr_offset_from)]
 #![feature(generic_const_exprs)]
 #![feature(const_refs_to_cell)]
 #![feature(const_trait_impl)]