so e.g. math font dialog doesn't react to button clicks.

since...

commit ab8e0f58
Author: Caolán McNamara <caolanm@redhat.com>
Date:   Fri Jan 18 17:08:58 2019 +0000

    Resolves: tdf#122484 replace gtk autocomplete with vcl-alike autoselect

remove the entrycompletions but left the reference to them

Change-Id: Ia02d0e657fc114692f69f88890192c470a1cab22
Reviewed-on: https://gerrit.libreoffice.org/69208
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>