Bug 17871: Remove zebra::snippet to allow access to facets in YAZ 5.8.1+

Bug 17871: Remove zebra::snippet to allow access to facets in YAZ 5.8.1+

This patch restores access to zebra facets (or zebra::snippet) with YAZ 5.8.1 or higher.

It was failing due to The <retrieval syntax="xml" name="zebra::*" /> entry in
retrieval-info-bib-dom.xml which IndexData said it wasn't even needed to
get that access.

Edit: I amended the commit message (tcohen)

Signed-off-by: Colin Campbell <colin.campbell@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
I tested on kohadevbox and found no regression or behaviour change. I
will provide a followup for the packages.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>