Address issues uncovered by rust-1.78 beta (#32130)

This change makes changes to allow Servo to compile with the 1.78
version of Rust:

 - Dead code is removd (Rust seems to have gotten better at detecting
   it).
 - The `FlowRef` `DerefMut` is updated according to @SimonSapin's advice
   [^1].
 - The `imports.rs` now explicitly silences warnings about unused
   imports.

[^1]: https://github.com/servo/servo/issues/6503#issuecomment-2066088179

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---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes do not require tests because they should not change
behavior.

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1 files changed, 0 insertions, 21 deletions

diff --git a/components/script/euclidext.rs b/components/script/euclidext.rs
deleted file mode 100644
index c6eb72f89fc..00000000000
--- a/components/script/euclidext.rs
+++ /dev/null
@@ -1,21 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
-
-use euclid::default::Rect;
-
-pub trait RectExt {
-    fn to_u64(&self) -> Rect<u64>;
-}
-
-impl RectExt for Rect<f64> {
-    fn to_u64(&self) -> Rect<u64> {
-        self.cast()
-    }
-}
-
-impl RectExt for Rect<u32> {
-    fn to_u64(&self) -> Rect<u64> {
-        self.cast()
-    }
-}