Bug 35044: (QA follow-up): Remove empty additional_field_values entries

Bug 35044: (QA follow-up): Remove empty additional_field_values entries

To test:
1) Follow any of the above test plans to add some
   additional_field_values entries
2) Run the following SQL:
  update additional_field_values set value = '';
3) Run updatedatabase twice. Notice the first time it tells you how many
   entries were removed. The 2nd time it does nothing.

Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>