Kill wp index accessibility Options fieldset spec

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Use mixin for hiding filters fieldset legend

This should be a more accessible approach.

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Kill rest of wp index accessibility fieldset spec

The filter fieldset no longer behaves like a toggable fieldset.

Signed-off-by: Alex Coles <alex@alexbcoles.com>