Remove useless tidy-alphabetical markers.

rustfmt already sorts `use` declarations within the same group.

compiler/rustc_fs_util/src/lib.rs

@@ -1,9 +1,7 @@
-// tidy-alphabetical-start
 use std::ffi::CString;
 use std::fs;
 use std::io;
 use std::path::{absolute, Path, PathBuf};
-// tidy-alphabetical-end
 
 // Unfortunately, on windows, it looks like msvcrt.dll is silently translating
 // verbatim paths under the hood to non-verbatim paths! This manifests itself as