This removes six separate warnings when building servo. One of
the warnings was an unused mut, and the other were various dead code
warnings
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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 fix#16584 (github issue number if applicable).
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- [ ] There are tests for these changes OR
- [X] These changes do not require tests because they address warnings from the build process
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Source-Repo: https://github.com/servo/servo
Source-Revision: f3c1bbe0700806ef2def3b0c5ce0dde4eba107ea
c4c63c006e