Bug 17916 - "Delete MARC modification template" fails to actually delete it

Bug 17916 - "Delete MARC modification template" fails to actually delete it

The MARC modification templates' 'Delete' button fails because the event
handler has a "preventDefault" but the outcome of the confirmation
function must return true or false.

This patch removes the "preventDefault" from the .delete_template click
handler as well as a redundant onclick attribute from the delete link
itself.

To test, apply the patch and go to Tools -> MARC modification templates.
Clicking the delete button for any existing template should work
correctly.

Followed test plan, worked as intended

Signed-off-by: Alex Buckley <alexbuckley@catalyst.net.nz>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>