fdo#80986: disable highlight DOCX import

Highlight support is not implemented fully, so
it seems better to disable DOCX import of it until
it is finished.
Highlight can't be modified on the UI and is not
saved to ODT/DOC (regression).

Regression from:
8b949134441056a1455d67ddfdd7e0bc5f2ee682

Change-Id: I94891769766ae90017e8afa70e65d080d5270202