delete badcat theme

[get-me-power]

Hi, Christian.
Look at this link.

https://github.com/emanuelrosa/badcat/tree/master/autoload/airline/themes

I think badcat theme should remove this repo.
Could you check this Pull Request?

Related PR

#200

[get-me-power]

@chrisbra
I want to merge this patch.
Is that okay?

[chrisbra]

thanks.

[get-me-power]

Thanks for checking this Pull Request.

[r888800009]

I think this merge is destructive for this repo theme diversity and backward compatibility, you should add some information to prevent people waste time a lot of time to find this issue to fix the problem, maybe check the theme is removed from vim-airline-themes and show hint, or in document highlight how to find the upstream.

[r888800009]

For example, I used the vice theme, and the airline would show the error Could not resolve airline theme "vice". Themes have been migrated to github.com/vim-airline/vim-airline-themes., this is not helpful.