Auto merge of #23532 - est31:unused_code_removal_4, r=emilio

Remove unused code (4/4)

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Fourth and final PR in a series of PRs to remove unused/dead code from servo, powered by an (upcoming) tool of mine. Please take a look and tell me if you want to keep something.

* First PR: #23477
* Second PR: #23498
* Third PR: #23499

Shortstat of the combined PR series:
```
47 files changed, 7 insertions(+), 805 deletions(-)
```

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `___` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors

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- [ ] There are tests for these changes OR
- [x] These changes do not require tests because they only remove dead code

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components/style/sharing/mod.rs

@@ -102,15 +102,6 @@ mod checks;
 pub const SHARING_CACHE_SIZE: usize = 31;
 const SHARING_CACHE_BACKING_STORE_SIZE: usize = SHARING_CACHE_SIZE + 1;
 
-/// Controls whether the style sharing cache is used.
-#[derive(Clone, Copy, PartialEq)]
-pub enum StyleSharingBehavior {
-    /// Style sharing allowed.
-    Allow,
-    /// Style sharing disallowed.
-    Disallow,
-}
-
 /// Opaque pointer type to compare ComputedValues identities.
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub struct OpaqueComputedValues(NonNull<()>);