rust: miscdevice: remove unnecessary import

`kernel::str::CStr` is included in the prelude.

Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Link: https://lore.kernel.org/r/20250704-cstr-include-miscdevice-v1-1-bb9e9b17c892@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

rust/kernel/miscdevice.rs

@@ -17,7 +17,6 @@ use crate::{
     mm::virt::VmaNew,
     prelude::*,
     seq_file::SeqFile,
-    str::CStr,
     types::{ForeignOwnable, Opaque},
 };
 use core::{marker::PhantomData, mem::MaybeUninit, pin::Pin};