Remove unused ScopeGuarding trait

As of commit 0441bdc634 (Remove ScopeGuard::commit in favor of drop,
2026-04-30), this trait is empty so there's not much use having it
for now.

src/parser.rs

@@ -30,8 +30,7 @@
 };
 use assert_matches::assert_matches;
 use fish_common::{
-    EscapeFlags, EscapeStringStyle, FilenameRef, ScopeGuarding, ScopedCell, ScopedRefCell,
-    escape_string,
+    EscapeFlags, EscapeStringStyle, FilenameRef, ScopedCell, ScopedRefCell, escape_string,
 };
 use fish_util::get_time;
 use fish_widestring::{WExt as _, wcs2bytes};
@@ -41,6 +40,7 @@
 use std::fs::File;
 use std::io::Write as _;
 use std::num::NonZeroU32;
+use std::ops::DerefMut;
 use std::rc::Rc;
 use std::sync::Arc;
 use std::time::Duration;
@@ -906,10 +906,7 @@ pub fn scope(&self) -> ScopedData {
     /// Modify the scoped values for the duration of the caller's scope (or whenever the ParserScope is dropped).
     /// This accepts a closure which modifies the ScopedData, and returns a ParserScope which restores the
     /// data when dropped.
-    pub fn push_scope<'a, F: FnOnce(&mut ScopedData)>(
-        &'a self,
-        modifier: F,
-    ) -> impl ScopeGuarding + 'a {
+    pub fn push_scope<'a, F: FnOnce(&mut ScopedData)>(&'a self, modifier: F) -> impl DerefMut + 'a {
         self.scoped_data.scoped_mod(modifier)
     }
 

src/reader/reader.rs

@@ -111,8 +111,8 @@
 use assert_matches::assert_matches;
 use errno::{Errno, errno};
 use fish_common::{
-    EscapeFlags, EscapeStringStyle, ScopeGuard, ScopeGuarding, escape, escape_string,
-    escape_string_with_quote, exit_without_destructors, get_obfuscation_read_char, help_section,
+    EscapeFlags, EscapeStringStyle, ScopeGuard, escape, escape_string, escape_string_with_quote,
+    exit_without_destructors, get_obfuscation_read_char, help_section,
     restore_term_foreground_process_group_for_exit, write_loop,
 };
 use fish_fallback::{fish_wcwidth, lowercase};
@@ -143,7 +143,7 @@
     cmp,
     io::BufReader,
     num::NonZeroUsize,
-    ops::{ControlFlow, Range},
+    ops::{ControlFlow, DerefMut, Range},
     os::fd::{AsRawFd as _, BorrowedFd, FromRawFd as _, OwnedFd, RawFd},
     pin::Pin,
     sync::{
@@ -424,7 +424,7 @@ pub fn reader_pop() {
     }
 }
 
-pub fn fake_scoped_reader<'a>(parser: &'a Parser) -> impl ScopeGuarding<Target = Reader<'a>> + 'a {
+pub fn fake_scoped_reader<'a>(parser: &'a Parser) -> impl DerefMut<Target = Reader<'a>> + 'a {
     let inputfd = -1;
     let conf = ReaderConfig {
         inputfd,