Fix warnings introduced in newer Rust Nightly

This does not (yet) upgrade ./rust-toolchain

The warnings:

* dead_code "field is never read"
* redundant_semicolons "unnecessary trailing semicolon"
* non_fmt_panic "panic message is not a string literal, this is no longer accepted in Rust 2021"
* unstable_name_collisions "a method with this name may be added to the standard library in the future"
* legacy_derive_helpers "derive helper attribute is used before it is introduced" https://github.com/rust-lang/rust/issues/79202

components/style/values/generics/effects.rs

@@ -35,7 +35,6 @@ pub use self::GenericBoxShadow as BoxShadow;
 
 /// A generic value for a single `filter`.
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
-#[animation(no_bound(U))]
 #[derive(
     Clone,
     ComputeSquaredDistance,
@@ -49,6 +48,7 @@ pub use self::GenericBoxShadow as BoxShadow;
     ToResolvedValue,
     ToShmem,
 )]
+#[animation(no_bound(U))]
 #[repr(C, u8)]
 pub enum GenericFilter<Angle, NonNegativeFactor, ZeroToOneFactor, Length, Shadow, U> {
     /// `blur(<length>)`