Bug 14316: Clarify meaning of record number in Batch record deletion tool

Bug 14316: Clarify meaning of record number in Batch record deletion tool

Changes the label from 'list of record numbers...' to
'List of biblionumbers or authority ids...' to make it
more clear to the user which kind of input is expected.

To test:
- Go to Tools > Batch record deletion
- Check the new description
- Decide if it's more clear or not

Signed-off-by: Marc Veron <veron@veron.ch>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>