i18n(ja): remove translations outdated by v6 changes

[morinokami]

Description (required)

These translations are no longer accurate due to major content restructuring in the v6 branch.

Related issues & labels (optional)

• Suggested label: i18n

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Tracked Files

File	Note
ja/basics/project-structure.mdx	Localization changed, will be marked as complete.
ja/guides/deploy/render.mdx	Localization changed, will be marked as complete.
ja/guides/fonts.mdx	Localization removed, will be marked as missing.
ja/guides/integrations-guide/sitemap.mdx	Localization removed, will be marked as missing.
ja/guides/migrate-to-astro/from-docusaurus.mdx	Localization changed, will be marked as complete.
ja/guides/migrate-to-astro/from-sveltekit.mdx	Localization changed, will be marked as complete.
ja/guides/migrate-to-astro/from-vuepress.mdx	Localization changed, will be marked as complete.
ja/guides/migrate-to-astro/from-wordpress.mdx	Localization changed, will be marked as complete.
ja/install-and-setup.mdx	Localization removed, will be marked as missing.

Warnings reference

Icon	Description
🔄️	The source for this localization has been updated since the creation of this pull request, make sure all changes in the source have been applied.

[sarah11918]

Thank you!! 🎉