Remove references to obsolete tools (Singularity, Susy…)

Singularity (named in Tools > Grid system part) is no more maintained, it must be removed from guidelines and use CSS Grid Layout instead. Source : https://snugug.com/musings/saying-goodbye-to-singularity/

Done with c8c2cea. Thanks!

Thank Kitty but I meant in Grid System text part for all langauges, eg. for english:

sass-guidelines/pages/en/_tools.md

Line 32 in c8c2cea

    
           If you are not tied to a specific grid system, you will be pleased to know there are two top-notch Sass powered grid engines out there: [Susy](https://www.oddbird.net/susy/) and [Singularity](https://github.com/at-import/Singularity). Both do much more than you will ever need so you can pick the one you prefer between these two and be sure all your edge cases&mdash;even the most nifty ones&mdash;will be covered. If you ask me, Susy has a slightly better community, but that’s my opinion.

Thanks, I messed up my code search and missed a lot of cases.

Susy is also deprecated https://www.oddbird.net/susy/
The whole "Grid systems" section should be updated.

And the last version of csswizardry-grids have almost 10 years with no significant update since then so I'm not sure to mention it in guidelines is good idea.
Grid systems tools/dependencies no longer seem useful since CSS3, I rename my issue.