Removed 'XML_lang' tag being auto-written in redline case

When there was a redline in a DOCX file that relates to formatting -
the DOCX exporter automatically assumed that if the 'after' properties
contains an 'XML_lang' node - then also the 'before' properties
should also contain the 'XML_lang' node - and this is wrong.

Change-Id: I383e10c11c228dd6847fd8eecb35c5c23c5f955e
Reviewed-on: https://gerrit.libreoffice.org/6900
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>