Bug 20559: Occurrences of loading-small.gif still exist

Bug 20559: Occurrences of loading-small.gif still exist

This patch removes some leftover references to a file which no longer
exists. In the OPAC, loading-small.gif was included in CSS which was
never used. In the staff client, loading-small.gif should have been
corrected to spinner-small.gif.

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

 - Submit a batch of records to modify
 - In the table of titles which will be modified, click the 'Show MARC'
   button.
   - The modal preview window should show "Loading" and an animated
     spinner before the MARC record is loaded.

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>