chore: remove Google Ads

[yoshinorin]

Check List

• [x] Others (Update, fix, translation, etc...)

Purpose

Remove google ads. IMHO, we should remove google ads from our site.

refs: https://github.com/orgs/hexojs/discussions/5375

Reasons

• The current active maintainers can't manage it (we don't have a permission)
• I assume google ads's revenue is very few and it not helpful us
• unfriendly to users

[github-actions[bot]]

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