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 https://github.com/KittyGiraudel/sass-guidelines/commit/c8c2cea0ee976a9680e36d02a3a1106dcf4c419b. Thanks!

Thank Kitty but I meant in Grid System text part for all langauges, eg. for english: https://github.com/KittyGiraudel/sass-guidelines/blob/c8c2cea0ee976a9680e36d02a3a1106dcf4c419b/pages/en/_tools.md?plain=1#L32

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.