Bug 15911: Use noEnterSubmit CSS class instead of prevent_submit.js

Bug 15911: Use noEnterSubmit CSS class instead of prevent_submit.js

This patch removes the use of a separate js file, prevent_submit.js, in
favor of using a CSS class to trigger the same functionality in
staff-global.js.

To test, apply the patch and test the following pages to confirm that
pressing "Enter" when the cursor is in any field in the main form does
not submit the form.

 - In Acquisitions, add to a basket from a new (empty) record
 - In Acquisitions, receive an order line
 - In Serials, locate a subscription and open the "Edit serials" page
   from the "Serial collection" page.

Signed-off-by: Hayley Mapley <hayleymapley@catalyst.net.nz>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>