[css-counter-styles] Define speak-as:auto for system:override styles. Eliminate 'computed to' wording, as there's no computed values in at-rules.

--HG--
extra : rebase_source : 6448f40d8b88b259ea14563c6438272c4a83e554
[css-counter-styles] Change decimal-leading-zero to use 'pad' rather than a fixed style.