remove Gallery.css (unmaintained since 2016) (#3704)

- ref. #3558

README.md

@@ -1575,7 +1575,6 @@ A [gallery](https://en.wikipedia.org/wiki/Gallery_Software) is software that hel
 - [Coppermine](https://coppermine-gallery.net/) - Multilingual photo gallery that integrates with various bulletin boards. Includes upload approval and password protected albums. ([Demo](https://coppermine-gallery.net/demo/cpg15x/), [Source Code](https://github.com/coppermine-gallery/cpg1.6.x)) `GPL-3.0` `PHP`
 - [Damselfly](https://damselfly.info) - Fast server-based photo management system for large collections of images. Includes face detection, face & object recognition, powerful search, and EXIF Keyword tagging. Runs on Linux, MacOS and Windows. `GPL-3.0` `C#/.NET`
 - [Fussel](https://github.com/cbenning/fussel) - Self-hosted, no-backend static photo gallery. Face tag recognition, albums and more. ([Demo](https://benninger.ca/fussel-demo/)) `MIT` `Python/Docker`
-- [Gallery CSS](https://benschwarz.github.io/gallery-css/) - Gallery.css is all CSS. Think: Simple, maintainable and understandable galleries without the use of Javascript. ([Source Code](https://github.com/benschwarz/gallery-css)) `MIT` `CSS`
 - [HomeGallery](https://home-gallery.org) - Self-hosted open-source web gallery to browse personal photos and videos featuring tagging, mobile-friendly, and AI powered image discovery. ([Demo](https://demo.home-gallery.org), [Source Code](https://github.com/xemle/home-gallery)) `MIT` `Nodejs`
 - [ImageStore](https://github.com/gregordr/ImageStore) - Self-hosted Google Photos alternative, with a very similar UI. ([Demo](https://gregordr.github.io/ImageStore/)) `Apache-2.0` `Nodejs/Docker`
 - [Immich](https://github.com/alextran1502/immich) - Self-hosted photo and video backup solution directly from your mobile phone. `MIT` `Docker`