Bug 27752: Correct eslint errors in batchMod.js

Bug 27752: Correct eslint errors in batchMod.js

This patch makes minor changes to batchMod.js in order to address errors
raised by ESLint. These changes include whitespace changes, so diff
accordingly.

To test, apply the patch and go to Tools -> Batch item modification.

- Submit a batch of barcodes for modification.
- Uncheck some checkboxes to hide columns in the table showing your
  submitted items.
- Return to the batch item modification page and submit your batch
  again.
- The columns you selected should still be hidden.
- Submit a batch of items for deletion.
- The same columns should be hidden here too.

To confirm that ESLint is happy with the changes you could open the file
for editing using an editor with ESLint integration, or install ESLint
on the command line:
https://eslint.org/docs/user-guide/command-line-interface

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>