Bug 37739: Adjust vendor deletion modal code after bootstrap 5 update

Bug 37739: Adjust vendor deletion modal code after bootstrap 5 update

This patch fixes a conflict between bug 31921 and bug 35402.

Test plan:
Create a vendor then delete it using the "Delete vendor" button
Confirm that the modal looks like other modals in Koha.
Click the "x", "No" and "Yes". Confirm that "x" and "no" close the modal
but "yes" correctly delete the vendor.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>