Drop repo's 'crystal-language' topic

[Matías García Isaía]

The Crystal community has somewhat decided to use crystal as the language's topic.

To avoid fragmentation in the community, please drop the crystal-language topic, that only has ~30 repositories at the moment. We're sticking to crystal, instead.

Any contributor can change it from the repo's homepage.

See crystal-lang/crystal#4241 for more context.

Thank you very much :)

[jasdeep singh]

done, thanks! @matiasgarciaisaia