Fix Markdown link (a) component

[tboby]

This confused me for a while as I thought I was using components wrong!

 Markdown.markdown [
      markdown.children rel.Description
      markdown.components [
          unbox<IComponent> (
              Interop.mkAttr "a" (fun (x: ILinkProperties) ->
                  Html.a [
                      prop.children x.children
                      prop.className "link"
                      prop.href x.href
                  ])
          )
      ]
  ]

works, which I assume is what linkReference is supposed to be overriding.

The table at https://github.com/remarkjs/react-markdown/blob/main/changelog.md#600---2021-04-15 implies that trow/tcell may be wrong too, but I didn't check that.