ReferentialVehicleJourneys: Fix line drop-down placeholder

After adding the `initvalue` data attribute, the placeholder was no
longer rendered. Fix this by:

1. Removing all elements from the collection to ensure that boolean
   options don't get added by default to the select
   (https://github.com/plataformatec/simple_form/blob/84e4465/lib/simple_form/inputs/collection_input.rb#L36-L41)
2. Not setting an `initSelection` on the Select2 config if the initial
   selection fields are empty.

This finally gets the placeholder to display correctly again.

Refs #5889

0 files changed, 0 insertions, 0 deletions