[ko] frontmatter key 삭제

[SnowMarble]

part of #7412 ko

남겨놓을 것:
title, slug, original_slug, l10n.*

지울 것:
위 남길 것 이외의 모든것을 지워야합니다. (tags, translation_of, browser-compact, spec-urls 등)

• games [ko] remove duplicated frontmatter keys - games #8303
• glossary [ko] remove duplicated frontmatter keys - glossary #8304
• learn [ko] remove duplicated frontmatter keys - learn #8306
• mdn [ko] remove duplicated frontmatter keys - mdn #8307
• mozilla [ko] remove duplicated frontmatter keys - mozilla #8308
• web [ko] remove duplicated frontmatter keys - web #8309
• webassembly [ko] remove duplicated frontmatter keys - webassembly #8310