Auto merge of #16757 - zombiefungus:issue16716, r=KiChjang

Remove obsolete paint threads option #16716

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Remove paint_threads from `ports/cef/core.rs` and `components/config/opts.rs`

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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 #16716

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