[REF] *: <a/> elements do not need the oe_link class

The 'oe_link' class is not linked to any style. The class is
automatically converted to 'btn-link' for <button/> elements but this
will not be done on <a/> elements as they are (nearly) unprocessed
node during views rendering.

Also there is minor difference between a '.btn-link' element and a
<a/> element anyway (and maybe there should not be at all).