Remove references to obsolete tools (Singularity, Susy…)

[Klemart3D]

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/

[KittyGiraudel]

Done with c8c2cea. Thanks!

[Klemart3D]

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—even the most nifty ones—will be covered. If you ask me, Susy has a slightly better community, but that’s my opinion.

[KittyGiraudel]

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

[Pasqualle]

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

[Klemart3D]

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.