Remove dead links to old kernel and std docs

content/docs.ar.md

content/docs.cz.md

content/docs.da.md

content/docs.de.md

content/docs.en.md

content/docs.eo.md

content/docs.es.md

content/docs.fr.md

content/docs.hu.md

content/docs.it.md

content/docs.jp.md

content/docs.ko.md

content/docs.nl.md

content/docs.no.md

content/docs.pl.md

content/docs.pt.md

content/docs.ru.md

content/docs.sv.md

content/docs.tr.md

content/docs.uk.md