Resolve dead code warnings on various platforms

[dtolnay]

warning: unused variable: `processes_to_update`
   --> src/unix/apple/system.rs:234:9
    |
234 |         processes_to_update: ProcessesToUpdate<'_>,
    |         ^^^^^^^^^^^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_processes_to_update`
    |
    = note: `#[warn(unused_variables)]` on by default

warning: field `bsd_name` is never read
  --> src/unix/apple/disk.rs:28:5
   |
25 | pub(crate) struct DiskInner {
   |                   --------- field in this struct
...
28 |     bsd_name: Option<Vec<u8>>,
   |     ^^^^^^^^
   |
   = note: `#[warn(dead_code)]` on by default

warning: type alias `RetainedCFString` is never used
   --> src/unix/apple/disk.rs:341:17
    |
341 | pub(crate) type RetainedCFString = CFReleaser<core_foundation_sys::string::__CFString>;
    |                 ^^^^^^^^^^^^^^^^

warning: constant `KIO_RETURN_SUCCESS` is never used
   --> src/unix/apple/macos/ffi.rs:171:11
    |
171 | pub const KIO_RETURN_SUCCESS: i32 = 0;
    |           ^^^^^^^^^^^^^^^^^^
    |
    = note: `#[warn(dead_code)]` on by default

warning: function `IOServiceMatching` is never used
   --> src/unix/apple/macos/ffi.rs:133:12
    |
133 |     pub fn IOServiceMatching(a: *const c_char) -> CFMutableDictionaryRef;
    |            ^^^^^^^^^^^^^^^^^

warning: function `IORegistryEntryGetName` is never used
   --> src/unix/apple/macos/ffi.rs:159:12
    |
159 |     pub fn IORegistryEntryGetName(entry: io_registry_entry_t, name: io_name_t) -> kern_return_t;
    |            ^^^^^^^^^^^^^^^^^^^^^^

warning: function `get_all_utf8_data_from_file` is never used
  --> src/unix/linux/utils.rs:15:15
   |
15 | pub(crate) fn get_all_utf8_data_from_file(file: &mut File, size: usize) -> io::Result<String> {
   |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(dead_code)]` on by default

warning: function `get_all_utf8_data` is never used
  --> src/unix/linux/utils.rs:22:15
   |
22 | pub(crate) fn get_all_utf8_data<P: AsRef<Path>>(file_path: P, size: usize) -> io::Result<String> {
   |               ^^^^^^^^^^^^^^^^^

warning: function `to_cpath` is never used
  --> src/unix/linux/utils.rs:88:15
   |
88 | pub(crate) fn to_cpath(path: &std::path::Path) -> Vec<u8> {
   |               ^^^^^^^^

warning: unused import: `self::ios as inner`
  --> src/unix/apple/mod.rs:15:24
   |
15 |         pub(crate) use self::ios as inner;
   |                        ^^^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(unused_imports)]` on by default

warning: function `display_ntstatus_error` is never used
   --> src/windows/process.rs:229:11
    |
229 | unsafe fn display_ntstatus_error(ntstatus: windows::core::HRESULT) {
    |           ^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `#[warn(dead_code)]` on by default

warning: method `account_name` is never used
  --> src/windows/sid.rs:59:19
   |
20 | impl Sid {
   | -------- method in this implementation
...
59 |     pub(crate) fn account_name(&self) -> Option<String> {
   |                   ^^^^^^^^^^^^
   |
   = note: `#[warn(dead_code)]` on by default

[dtolnay]

The last use of this function was deleted in #1316.

[GuillaumeGomez]

Thanks!