fix(theme-classic): remove breadcrumb items without href from microdata

[Josh-Cena]

Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.
• If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

Motivation

This has caused too much confusion, both on Discord and on the issue tracker (#7303, #7241). Even when I tend to think it's working as intended, let's remove it from the default theme to conform to the one and only truth™ in search engines.

Test Plan

Tested on rich results; it's valid now.

[netlify]

✅ [V2]

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[github-actions]

⚡️ Lighthouse report for the changes in this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
https://deploy-preview-7304--docusaurus-2.netlify.app/	🟠 55	🟢 100	🟢 92	🟢 100	🟢 90	View report
https://deploy-preview-7304--docusaurus-2.netlify.app/docs/	🟠 61	🟢 94	🟢 92	🟢 90	🟢 90	View report

[github-actions]

Size Change: 0 B

Total Size: 804 kB

ℹ️ View Unchanged

Filename	Size
website/.docusaurus/globalData.json	50.7 kB
website/build/assets/css/styles.********.css	105 kB
website/build/assets/js/main.********.js	610 kB
website/build/index.html	38.8 kB

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[slorber]

🤷‍♂️ google seems to like this better 👍