Remove preselection and force the user to select the destination group

Problem

As reported by a user, when migrating with direct transfer, having the destination group preselected might lead to mistakes.

Proposed solution - TBD

Remove preselection and force user to select a destination group instead of defaulting to some group and hoping the user remembers to change it.

User comment: "If it makes sense to have this filled depends on how one navigates to the import page IMHO."