Consider if XSL references can be removed

SVG 1.0 used several XSL properties and property values which have since been integrated into CSS.
SVG 2 refers several times to "CSS or XSL" properties. This may make the reference to XSL unnecessary.

The sole exception may be the 'dominant-baseline' property, which doesn't yet seem to be in CSS. We should see if this is supported in implementations, and consider dropping it.