All RTL_CONSTASCII_USTRINGPARAMs removed from canvas

Change-Id: Ie62d080eb58a05f7bb18aa1cc2f518c951145460
Reviewed-on: https://gerrit.libreoffice.org/2283Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>