Restore redirect for former SDEX liquidity pools URL

[JFWooten4]

The former liquidity page URL now returns a 404 instead of redirecting to the current page.

Old URL:
https://developers.stellar.org/docs/learn/encyclopedia/sdex/liquidity-on-stellar-sdex-liquidity-pools

Current canonical URL:
https://developers.stellar.org/docs/learn/fundamentals/liquidity-on-stellar-sdex-liquidity-pools

Expected behavior

Requests to the old /docs/learn/encyclopedia/sdex/... URL should redirect to the current /docs/learn/fundamentals/... page so existing inbound links and bookmarks continue to work.

Actual behavior

The old URL currently returns 404 Not Found.

This appears to be a regression in the redirect coverage after the docs path was reorganized.

[kaankacar]

🤖 Automated message from Kaan's Automated Triage Bot.

No maintainer assigned this issue, so I did not work it.

Assign @kaankacar, @ElliotFriend or @wmendes if you want me to open a PR for it.

[ElliotFriend]

Great catch! Have a fix ready in #2858. found some redirects that were going to the wrong SDEX page, while i was in there.