Remove check for "min-width:auto"/"min-height:auto" as part of flexbox section, since these values were recently removed from the flexbox spec.

Remove check for "min-width:auto"/"min-height:auto" as part of flexbox section, since these values were recently removed from the flexbox spec, in this spec-edit: https://dvcs.w3.org/hg/csswg/rev/9437131b3d6e