fix : il ne faut pas contraindre la taille des SVG

(et plus généralement des images vectorielles)

Co-authored-by: RealET <real3t@gmail.com>
Refs: https://git.spip.net/spip/medias/pulls/4893


Co-authored-by: RealET <realet@noreply.git.spip.net>
Co-committed-by: RealET <realet@noreply.git.spip.net>