Backport from master, squashed in:

- gpg4libre: Init xmlsec in one place before creating the services
- xmlsecurity: fix loplugin:unusedvariablecheck warning
- xmlsecurity: fix loplugin:passstuffbyref warnings
- xmlsecurity: remove newly introduced redundant namespace alias, used only once

Change-Id: I46a05074706bba77ebc488f0df296e35e2b7d553
Reviewed-on: https://gerrit.libreoffice.org/39096Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
Tested-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>