docs: fix wording in removed-sites notes

[kuishou68]

Summary

• fix several spelling and grammar mistakes in docs/removed-sites.md
• keep the patch documentation-only with no behavioral changes
• preserve the original meaning of each site-removal note while improving readability

Self-review

• limited the edits to clear wording mistakes rather than rewriting the historical notes
• checked the diff to avoid accidental formatting churn outside the touched lines
• kept the scope narrow so the PR is easy to review and low risk

Closes #2862