Bug 27754: Correct eslint errors in basket.js

Bug 27754: Correct eslint errors in basket.js

This patch makes minor changes to basket.js in the staff interface
templates in order to quiet warnings from ESLint. Besides whitespace,
most changes are to correct undeclared or unnecessarily declared
variables.

To test, apply the patch and verify that the cart still works
correctly.

 - Perform a catalog search in the staff interface.
 - Test adding single or multiple items to the cart from the search
   results page.
 - Testing adding and removing titles to the cart from the bibliographic
   detail page.
 - Open the cart and test the various controls in the toolbar to confirm
   that they still work correctly.

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>