After the gettext migration there is no point to have two
APIs for reading the same .mo file.

This patch is for sc/source/ui/[m-u]* for easier review.

Change-Id: I326902a89b8c65e32a42c3ebb55bea3609d32db6
Reviewed-on: https://gerrit.libreoffice.org/54136Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>