Bug 32865: Fix cataloguing/value_builder/unimarc_field_146a.pl

Bug 32865: Fix cataloguing/value_builder/unimarc_field_146a.pl

Remove unnecessary call to event.preventDefault()

This is part of the refactoring happening in bug 30975

Test plan:
1. Verify that the plugin continues to work as before

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit f1a27df97ec96dc6c6484a91268b1eae9c049f39)
Signed-off-by: Jacob O'Mara <jacobomara901@gmail.com>