SVG XLink attributes are not global attributes

[Elchi3]

The xLink attributes are not global to all SVG elements. They only apply to (many) SVG elements. However, these attributes are deprecated and not part of SVG 2. I think it is fine to remove them. svg.elements.a has some of them and if anyone ever feels strongly, we can accept a PR to add them to the other elements as well, but I think it is not worth it right now.

MDN says the following elements can have these attributes, so this would be a lot of new entries for little value IMO.

<a>
<animate>
<animateMotion>
<animateTransform>
<cursor>
<feImage>
<filter>
<font-face-uri>
<glyphRef>
<image>
<linearGradient>
<mpath>
<pattern>
<radialGradient>
<script>
<set>
<textPath>
<tref>
<use>