Bug 28193: OpacLoginInstructions news block broken by Bug 20168

Bug 28193: OpacLoginInstructions news block broken by Bug 20168

This patch fixes a regression which was introduced by Bug 20168, causing
the OpacLoginInstructions template code to revert back to the old system
preference behavior. This patch returns the correct markup.

To test, apply the patch and view the OPAC login page
(/cgi-bin/koha/opac-user.pl)

 - With no news entry for OpacLoginInstructions you should see the
   default: A block of text with two headings, "Don't have a password
   yet?" and "Don't have a library card?"
 - Go to Tools -> News and create an entry for OpacLoginInstructions.
 - Return to the OPAC and confirm that your custom text appears.
 - Try updating/installing another translation and adding a different
   news entry for that language. Confirm that the correct entry appears.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>