chore(lint): remove obsolete spec exceptions

[caugner]

Summary

Updates the spec_url exception list, removing two no longer used entries.

Also extracts this exception list to a lint/common/spec-url-exceptions.txt, without requiring approval from @mdn/engineering.

Test results and supporting details

Checked that the other ones are all still in use, and not in web-specs.

Related issues

Triggered by #29582 (comment).

[github-actions]

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[caugner]

I realize updates to spec url exceptions shouldn't require approval from @mdn/engineering, so I pushed 02c74a5 to extract it to a text file, and exclude it from CODEOWNERS (this also affects the standard track exceptions).