Do not force downloading Montserrat font from google

As for now, if you insert `ui.css` into your project it will force browser to download font file from google CDN. 
I think we should remove this because of 2 reasons:
- if someone wants to use our UI-Kit with some other fonts in a project
- this approach kills optimizations like next/fonts when you self-host fonts to get better performance and minimize layout shift.