...just like sdt controls already turned off design mode.

I'm not sure why design mode wasn't entirely turned off
right from the start, but I don't want to do that now because
forms are becoming more prominent in Writer. If design
mode is ALWAYS turned off for .docx files, then the workflow
will be different for *new* forms, since writer defaults to on.

Change-Id: I91c771f1ebd5e640da8067d38cb06076d8c50d5a
Reviewed-on: https://gerrit.libreoffice.org/62491
Tested-by: Jenkins
Reviewed-by: Justin Luth <justin_luth@sil.org>