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This PR renames the `js` dependency to `mozjs', ready for when https://github.com/servo/rust-mozjs/pull/377 lands.
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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 refactoring
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Source-Repo: https://github.com/servo/servo
Source-Revision: 5b36b74c06232a6436409b5fb474abf271a9e6f7
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