Remove Sist2 Demo link (website down) (#3807)

- ref. https://github.com/awesome-selfhosted/awesome-selfhosted/issues/3558
- https://sist2.simon987.net/ : HTTPSConnectionPool(host='sist2.simon987.net', port=443): Read timed out. (read timeout=10)

README.md

@@ -1720,7 +1720,7 @@ A [search engine](https://en.wikipedia.org/wiki/Search_engine_(computing)) is an
 - [MeiliSearch](https://www.meilisearch.com) - Ultra relevant, instant and typo-tolerant full-text search API. ([Source Code](https://github.com/meilisearch/MeiliSearch)) `MIT` `Rust`
 - [OpenSearch](https://opensearch.org) - Open source distributed and RESTful search engine. ([Source Code](https://github.com/opensearch-project/OpenSearch)) `Apache-2.0` `Java`
 - [Searx](https://searx.github.io/searx/) `⚠` - Privacy-respecting, hackable metasearch engine. ([Demo](https://searx.space/), [Source Code](https://github.com/searx/searx)) `AGPL-3.0` `Python`
-- [sist2](https://github.com/simon987/sist2) - Lightning-fast file system indexer and search tool. ([Demo](https://sist2.simon987.net/)) `GPL-3.0` `C`
+- [sist2](https://github.com/simon987/sist2) - Lightning-fast file system indexer and search tool. `GPL-3.0` `C`
 - [Typesense](https://typesense.org) - Blazing fast, typo-tolerant open source search engine optimized for developer happiness and ease of use. ([Source Code](https://github.com/typesense/typesense)) `GPL-3.0` `C++`
 - [Whoogle](https://github.com/benbusby/whoogle-search) `⚠` - A self-hosted, ad-free, privacy-respecting metasearch engine. `MIT` `Python`
 - [Yacy](https://yacy.net/en/index.html) - Peer based, decentralized search engine server. ([Source Code](https://github.com/yacy/yacy_search_server)) `GPL-2.0` `Java`