Bug 33277: Adjust source file for zebra mappings

Bug 33277: Adjust source file for zebra mappings

The previous patches adjusted the mappings directly - moving this
change to the correct build file

Not needed for sign off, but QA can test that nothing changes when rebuilding the files:
xsltproc etc/zebradb/xsl/koha-indexdefs-to-zebra.xsl etc/zebradb/marc_defs/marc21/authorities/authority-koha-indexdefs.xml > etc/zebradb/marc_defs/marc21/authorities/authority-zebra-indexdefs.xsl

Signed-off-by: Frank Hansen <frank.hansen@ub.lu.se>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>