Bug 37252: Use our local copy of MARC21slimUtils.xsl in MARC21slim2MADS.xsl

Bug 37252: Use our local copy of MARC21slimUtils.xsl in MARC21slim2MADS.xsl

Our local copy of the Library of Congress stylesheet MARC21slim2MADS.xsl is
our only one which includes MARC21slimUtils.xsl directly from the Library of
Congress rather than including our local copy. That makes it a fragile canary
for whatever reason that it currently isn't loading, but because it's not
exactly the most popular menu choice in all of Koha, it's far from being one
that anyone will notice.

We should instead include our local copy, make the bug 29556 change to
MARC21slim2MADS.xsl, and if someone wants to notice when including xsl from
LoC fails, they should write a test for it rather than depend on someone
noticing that saving authority records as MADS fails.

Test plan:
1. Without the patch, Authorities - search for Smith - click the linked
   name of any result to show authorities/detail.pl
2. Save - MADS (XML)
3. Check your downloaded file, see that it is zero bytes
4. Apply patch, restart_all
5. Repeat step 2, but this time find that your downloaded file is more
   than zero bytes.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Pedro Amorim <pedro.amorim@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>