Bug 17211: Remove use of onclick from OPAC fines page

Bug 17211: Remove use of onclick from OPAC fines page

To test:
1) Set the EnablePayPalOpacPayments syspref to Allow and the
PayPalSandboxMode to the appropriate mode
2) Go to OPAC fines
3) Confirm clicking the PayPal image link works the same before and
after the patch (opens pop up window)

Sponsored-by: Catalyst IT
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>